If you want to be able to playback 720p without worrying you're gonna need:
A new CPU and Motherboard! And the new motherboard may not be compatible with your RAM so probably new memory. Hmm, you may need a new pci express video card too( if yours is AGP )
A nice Core2Duo would be ideal but most dual core Intels or AMD cpu's should be fine for 720p.
If your on a tight budget the older Dual core chips can be had quite cheap.
check out
http://www.scan.co.uk/todayonly/If you want 1080p in the future then you need to look at something like a Intel E8400 or whatever AMD's equivalent is these days

oh, the 30FPS and 25FPS will just be because one is NTSC and the other PAL