I run 2000 professional on a Sony Viao originally preloaded with Win 98 and upgraded to 2000. On instaling SP2 many of my drivers would not work. No matter what I couldn't get my modem to operate (searched all over for a new driver inc. Sony etc). Got some help from Microsoft but in the end I had to install a second operating system. (NB: SP2 wouldn't uninstall)
I never risked loading SP2 on the new system. However now I've got a different modem (ADSL) and I'd rather be more uptodate with the SP's.
Is it worth the risk? I don't have time to spend hours sorting out problems. Eventually I'm getting a new PC and XP anyway.