I have twol DV cameras (Canon GL2, Panasonic PV-Gs150), and those work great in Premiere 2.0.
I just bought a mini Sanyo 1080p cam and the .mp4 files that I add in Premiere are choppy and I am unable to edit effectively. The export to Mpeg works fine and the video looks good, but the computer can't seem to handle it. Also Premiere 8.0 works just as poorly. Here are my specs:

Intel (2CPU) 6300@ 1.87Ghz, 1.86Ghz
3GB Ram (upgradeable to 4GB system memory) DDR2-667/DDR2-533/DDR2-400 Mhz
Nvidia GTX260 Video
Mother board is a P5LD2

Should I buy a new system or more RAM?