I would use the p3 system running windows 2000 as it has alot more going for it with that operating system .
Pci capture cards are not bad , but the pci design is limited in input bandwidth , however it is good if capturing at 352x288 , which is mpeg1 . I have a fly 3000 on an Amd xp1800 system and the best I can get is 352x288 and costs around $90.00 .
There are some pci cards which have dedicated mpeg 1 and 2
compression , but some of these cards get pricey .
Have a good look around for pci cards with mpeg 1 and mpeg 2 support , they have come down in price . and a good note is many of them will work under windows xp .
Agp capture cards are top of the line , but it depends on how much you want too spend here .
A good card with video capture would be 128MB ASUS V9280S2 GF4 Ti4800SE , at a cost of $280.00 , but your motherboard needs too support the 3.3 volt requirement too properly function .
Under windows xp may be a whole different thing as the agp slot is reported as a pci .
I have one 16mb tnt vivo card , it runs and plays games under xp , but even with the latest drivers for it , the system reports no capture device found (yes , there are xp drivers for this old card) .
Error : between motherboard and agp slot .
I never found out why , but because I use a dual boot system , I capture in windows 98 se , in your case it would be under windows 2000 .
If this all seem's a little too much , you can find plenty of resource's at
http://www.doom9.org/ , including the forum , which may answer many of the questions you might have .
That's the place I visit every now and then for handy information , with recommendations for video capture cards , software , and FAQ's and guides on how too capture .
Note : If you want tv tuner , the best sollution I found for my capture cards was too , define 1 clear channel for all capturing , and use my vcr as the tuner .
The vcr is used too switch between channels .
Note : The fly video 3000 pci card comes with a loop back cable for sound , it plugs between your sound card and itself . I highly recommend not too use such cables as they cause video garble when watching and recording .
Because you have a p3 and athlon system , you can use pci capture card for video side , and your sound card for the audio input as both systems have plenty of cpu power .
I only found the loop back sound card handy if you want too watch tv on your pc , as the sound is then passed too your pc speakers .
The inbiult tv tuners in many cards are extremely poor , that's just the way they are .
Hope this helps in your decission