Yentas With Attitude
Perhaps a play on the seminal hip-hop group N.W.A. ("Niggaz With Attitude")
Not like Pynchon to explicitly define jargon (hash total and Luhn checks slip past without comment on the very next page).
Consecutive invoice numbers. Hash totals that don't add up. Credit-card numbers failing their Luhn checks.
If you were looking over invoice numbers, they'd be more random, not numbered consecutively. Consecutive invoice numbers imply someone was just making them up in order, as the probability is they wouldn't be in consecutive order.
A "hash total" is just a batch total done on one or more numeric fields which appears in every record. This is a meaningless total, e.g., add the Telephone Numbers together for a number of Customers. It is used as a verification device for documents or records. For example, the dates of letters in a file may be added and separately noted as hash total. Thereafter, to ensure that no letter has been misfiled or substituted, the dates are re-added and the new total is compared with the hash total. Wikipedia
The Luhn algorithm or Luhn formula, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers in US and Canadian Social Insurance Numbers. It was created by IBM scientist Hans Peter Luhn and described in U.S. Patent No. 2,950,048, filed on January 6, 1954, and granted on August 23, 1960. Wikipedia
aka phony baloney
Traditional Russian song used as a musical track on Tetris. Pynchon also referenced Tetris in Against the Day  Hear it.
the plaintive folk tune
Referring to the song above.
just downloading some shit, 56K's a awesome speed
In reference to 56Kbit/s, a moderate speed at the time for downloading from a file sharing website like, say, the immensely popular Napster.
Interface cables; at the time RS232 was the standard for connecting modems, printers, mice, etc to pc's. Today, these connectors are mostly obsolete, having been replaced by USB and other faster standards.
the li'l goombas of Web design
a reference to Super Mario Bros.
Zima's the bitch drink of the nineties
This lemon-lime malt beverage was immensely popular in the years following its 1993 debut by Coors. It eventually gained a reputation as a girl's drink and was discontinued in 2008. Wikipedia entry
Fabian's Bit Bucket
In computing, the bit bucket is jargon for where lost computerized data has gone, by any means; any data which does not end up where it is supposed to, being lost in transmission, a computer crash, or the like, is said to have gone to the bit bucket — that mysterious place on a computer where lost documents go, as in: "What happened to that important spreadsheet that I was just editing?" OR "Oh, it went into the bit bucket." Wikipedia entry
The New York World Wide Web Workers e-mail list the WWWNY (or “Winnie”) list circulated among 2,000 Web professionals in New York in the web's early days, and was a good place to hunt for freelance assignments. The Winnie list also provided a forum for a lot of quirky blowhards to rant endlessly about Aggro Software’s browser or attack NetScathe’s flaky table support &c &c.
A physician whose subway ads were all over the NYC subway for over 30 years.
Bill Gates ... Microsoft
At the time, among computer geeks, Microsoft was the embodiment of all evil, and its CEO Bill Gates was the devil incarnate. (Bill Gates retired in 2008, so this was long before the Bill and Melinda Gates Foundation became the world's largest charitable foundation)
a single over on Rikers
a year in prison
Urban dictionary: Originating in the early 1980's, leet speak was first used by hackers as a way to prevent their websites/newsgroups from being found by simple keyword searches.
Time is what the Stones call on their side, yes it is.
"Time Is on My Side" is a song written by Jerry Ragovoy (under the pseudonym of Norman Meade)and made famous by the Rolling Stones in 1964. The chorus: "Time is on my side, yes it is."
the kind of barrel that holds 42 gallons
Crude oil in the U.S. is measured in barrels (1 bbl = 42 U.S. gallons)
Trichology is the branch of dermatology that deals with the scientific study of the health of hair and scalp. Trichologists themselves are not normally licensed healthcare workers, although members of the medical profession can undertake courses and/or careers within trichology. Trichology can be used in forensic studies of hairs to find suspects. Forensic trichology can determine the approximate age, body mass, race, and other important traits of the hair's owner. Trichologists are loyal to the academic study of hair loss science. http://en.wikipedia.org/wiki/Trichology
a lemon-lime alcopop haze
The reference is to the Zima drink, of a class of what is called “alcopop," very sweet alcohol drinks which are popular with young people. Zima has a lemon-lime flavor. Wikipedia
The sleazy old Deuce she remembers from her less responsible youth is no more, Giuliani and his developer friends and the forces of suburban righteousness have swept the place Disneyfied and sterile.
Pynchon is referencing here the school of thought claiming "Disney Saved Times Square", charting the dramatic increase in tourism and cost of billboard space in NYC's famed epicenter along with the production of a string of long-running, highly profitable, and artistically restrained Disney musicals. Through Maxine's mention of "the old Deuce", Pychon expresses his preference for the seedier Times Square, as it is perhaps found in "V".
Times Square Redevelopment (NYTimes)  Disney Theatrical (Wikipedia)