Well if you look at uptime records on netcraft.com the current record holder is FreeBSD with 1693 days of uptime (no reboots or anything, continous 24/7 operation incase you don't know... which most of you do, just a FYI for the uneducated)
That's 4.6 years of actively serving content on the internet. (website is
www.daiko-lab.co.jp) So that's close to 5 years.
Unfortunately Linux is one of those OSes whose uptime clock cycles back to zero after 475 days, so it's hard to tell how much uptime the longest running Linux server has. My personal record was 6 months and some days before a power outage knocked out a old Prolient (cpu was a pentium overdrive (86mhz I think) in place of the old 486DX) SCSI server I had sitting around.
The longest uptime for a windows 2000 internet server is
www.baltimore.com and is right now 783 days.
I find that kinda odd, since you need to reboot windows to apply security patches. BSD and Linux you don't have to reboot for anything, you just patch and restart the service. Unless you need to change the kernel or hardware or something of course.
But I guess they know what they are doing, they use a firewall that they themselves designed to protect the server. (they are a security company) So if they haven't been hacked and never figured it out, it's a pretty impressive feat.
Oh, and as far as WinXP fixing the problems of Win98's horrid memory management, they've fixed it. WinXP is based off of Win2k/NT. Could be called Windows NT 5.5 desktop edition and still be accurate and it's pretty stable. Maybe a slight degragation of performance over a couple weeks of being up, but it's insignificant compared to older win9x OSes.
Pretty rare to reboot or get blue screens, but IE has big issues with internet spyware/adware/malware/pop-up programs and stuff, very vunerable. I have to regularly clean that crap off of my parents computer. I use Adaware (free spyware removal tool) with a virus scanning program to scan my parent's computer every other week or so and that seems to catch everything.