<< Basic routing can be done pretty quickly in win2k, and even more quickly with winXP. >>
are there changes to the tcp/ip stack in XP that i should know about? im gonna run some throughput tests, but i dont believe there should be any performance gain. not to mention any gain, will be entirely unnoticeable in 99% of the environments you run it.
as far as addressing the post. win2k/xp (assuming u have hardware to run them) can do ICS easily. its effective for home users, but u might look into automate update patches and a personal firewall (i personal find them horrendously insecure). if youre gonna use windows, make sure you keep your patches bleeding edge (which has its own problems). and dont store anything secure on your router.
bsd/linux would be a great solution. floppy-based linux router distributions (freesco, coyote, lrp) on 386s w/ 16mb of memory accomplish everything ICS does, best part is you wont need a hard drive. ive never realy audited the performance of these boxes but i never felt a drop in performance when i switched from win2k adv server gateway functions to a trash 386 running linux. i dont think u will either. im sure theres a limit to what the 386 16mb memory can handle, but u wont reach that in home/small office use (unless youre maybe a warez junkie and have a fat pipe > T1/highspeed DSL. another advantage of linux is *COST*. if u have an old machine, u can run linux. youll most likely have to buy a new machine for windows. 2.4 kernel with iptables has a tremendous wealth of security features, if u want to take the time and secure it.
openbsd would be a strong choice. bsd allows you to securely secure your security. did i mention security? although, honestly, ive never used bsd extensively. linux is more where my experience lies, but bsd should be easy to learn.
those linksys routers are ok. there nothing to write home about, just any idiot can set one up.