this thread recently revived from 22-11-05, but OP (brucie888) profile indicates last visit jan 2009, so it might be interesting to see followup, intended usage, etc.
anyway, my approach would be: if can scrounge up parts, then:
1 check RAM limits by searching mobo on hp.com.
2 HDD gb limit could come from watching bios version during powerup, and possibly hp has bios update (OTOH, the update may be irrelevant). then search bios capability.
256MB is good for a PII, IMO|IME (win98 though, heh heh).

I lack suggestion for *nix browser that pampers gmail, but opera runs light on old win PCs. never tried it with gmail, cuz gmail looks a mess. also, try fastmail instead of yahoomail. so far fastmail's "old" interface relies less on weird scripts, so i recommend the old interface.

neil1982 suggest to install USB controller plus bootfloppy (pre-2001 (2002? 2003?) bios won't boot from USB) is interesting IMO...

i'm currently installing jaunty to older pc (no USB boot, and cranky cdrom). after much hunting, i found critical step is to get grub working. majority of the procedure here:
http://ubuntuforums.org/showthread.php?t=28948
this doesn't use a floppy (which i'd have welcomed)
maybe adapting this procedure would allow install from??? maybe copy install iso to HDD, then edit menu.lst so after boot HDD, menu.lst mounts the iso??

another thread with similar(?) method
http://ubuntuforums.org/archive/index.php/t-29358.html

in both cases, maybe temporarily slave the HDD into newer pc, to extract the iso's files to the HDD. then put HDD back into old pc.