The Radeon 2900XT has an S-video connector.
The 2900XT with 512MB of GDDR3 uses 161W at peak load.
The 2900XT with 1GB of GDDR4 uses 150W at peak load.
ATI recommend a minimum PSU power of 550W with 2 6pin PCI-E plugs.
You are probably better off going with a newer, faster and more power efficient card.