When I watch a Gaga music video from her official website it is offered in HD at 720P or 1080P. I can watch the 720P widescreen with no problem, but when I try and watch at 1080P I only get one frame per second. Is this because of my video card limitations, or my DSL limitations, or my LCD monitor limitations? The music always plays perfectly.
My video card: BFG GeForce 7300 GT 512 MB memory 8X AGP
My DSL: 5056 Kbps download
My LCD monitor: Samsung SyncMaster 242 MP (max resolution is 1920 x 1200 32-bit 60 HZ)
My sound card: Creative SB X-Fi Xtreme Music Platinum Sound Card
On a serious note; your system should be able to play 1080p. Try another video on youtube in 1080p (e.g. new divide by linkin park). If it still doesn't work, try playing a 1080p movie file on your PC (e.g. H.264), there's plenty of 1080p test files out there (just search google).
EDIT: re-read your post and your CPU is....well, ancient. I wouldn't be surprised if that's the reason. Upgrade your CPU.