http://exuberant.ms11.net/98sesp.html
^^ Update pack for Win98SE, contains almost every patch.
Install Win98SE on a machine, run DX9 and IE6 installs, then all the drivers, then the update pack, download the last few patched via Windows update, then run IE Eradicator.
http://www.litepc.com/ieradicator.html
Kill IE6 except the web view shell integration.
Install Opera browser, I have version 10.53 which works, 10.60 didn't work for my 98SE machine, maybe 10.61 will (bug maybe)
http://www.opera.com/
Install Clam Win
http://en.clamwin.com/
Why Clam Win? It doesn't have a real time scanner/whatever so it doesn't take much resources, useful when running it on a Pentium 166MMX with 128Mb RAM or so...
Install Pegasus mail client, works lightning fast and its tiny resource wise.
http://www.pmail.com/
For IM's Miranda IM
http://www.miranda-im.org/download/
Registry maintenance: Easy cleaner
http://personal.inet.fi/business/toniarts/ecleane.htm
Firewall
http://www.oldversion.com/download_ZoneAlarm_2.1.html
Yes this is OLD no! ancient! but it works well on ancient machines.
http://www.oldversion.com/ZoneAlarm.html
More versions, you can try to find the right bloat/moderness balance for your machine.
MP3 playback
http://www.oldversion.com/download_Winamp_2.95.html
Winamp 2.95 again ancient but what the heck so is my machine.
http://www.oldversion.com/
^^ useful site, all kinds of old stuff.