No usb tuners work on xp as of now.
Stay away from them anyway due to the bandwidth issues the others already said.
I use the Hauppauge win-tv go, its only mono but cheap and works every time all the time unlike my old ati tv wonder (stereo) where the drivers and software were horrible and the newer ones you had to hunt down and hack on to get to even work and then they still required mumbo jumbo like clicking on start the tv tuner and really quickly before it starts clicking anywhere else on the screen..
Yes thats no bull****. Even if you use a ati vid card with a ati tv tuner, same issues.
Stay away from ati period. but esp their tuners. Hauppauge or Leadtek actually has the best one on the market with spectacular reviews, its a bit more expensive but has a remote, is stereo, has fm tuning, and more vcr-like features.
One last word of advice dont use a tv tuner on a VIA based motherboard, it will work but I dont suggest using many if any pci cards in via based boards (I use one and I have pci issues).
Your safe with a SIS based board, nforce or AMD.
P4 is like a mustang, real slow but with a rocket on it its fast, but you still wouldn't want one!