Netflix - Hardware that works with Silverlight??

Hello,
I have a fairly basic recycled industrial computer:

3.00 gigahertz Intel Pentium 4
16 kilobyte primary memory cache
1024 kilobyte secondary memory cache
Hyper-threaded (2 total)
Board: Springdale-G
Bus Clock: 200 megahertz
BIOS: Phoenix Technologies, LTD 6.00 PG
1528 Megabytes Usable Installed Memory
Slot 'A0' has 1024 MB
Slot 'A1' is Empty
Slot 'A2' has 512 MB
Slot 'A3' is Empty

I've been using it to play HD audio and watch films via VLC for a while fine. but I recently started using Netflix (uk) and the picture is all choppy. I've done a bit of googling and it seems that the likely culprit is the old Radeon 7000 Graphics card and Silverlight not getting on. The option to turn on hardware acceleration is grayed out in silverlight for one thing.
I doubt I'll ever be able to watch the HD content on this machine but I'm hopeing a cheap graphics card might make the standard def stuff play ok.
Has anyone any experience with this? I'm wondering what type of card I should get so I can connect to a HDMI port and get a smooth play back. any help appreciated. Thanks in advance.
J