System Requirements for the 4350
PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard
300 Watt or greater power supply (350 Watt for ATI CrossFireX™ technology in dual mode) is recommended
Certified power supplies are recommended. Refer to http://support.amd.com/us/certified/power-supplies/Pages/listing.aspx for a list of Certified products
1GB of system memory recommended
Installation software requires CD-ROM drive
DVD playback requires DVD drive
Blu-ray™ playback requires Blu-ray drive and full 1080p display requires a 1080p-capable monitor
For Microsoft DirectX® 10.1 support, Windows Vista® Service Pack 1 is required
To enable dual mode ATI CrossFireX™ technology, a second ATI Radeon™ HD 4350 Series graphics card, and an ATI CrossFireX Ready motherboard are required
If you are upgrading the PSU I would consider something like 500 Watt. There will not be too much difference in price between that and a 300Watt and if you decide in the future, to upgrade the video card again, at least your PSU would probably cope.