Well, who knows, the system may be old enough that it just will not run Ubuntu without a lot of glitches. To be on the safe side, 256MB of RAM is an absolute minimum. Anything less calls for a more light-weight distribution. And of course, if the computer has an older video card, it may not be supported by the current nvidia drivers.

Update:
Well I downloaded Linux Mint (ubuntu with everything bolted on and nicer menu) and its working happily on my computer. I installed it on the other computer (on which ubuntu was stuffed) and it shed a lot of the problems that arose with ubuntu, but the nvidia-screen-res issue remained. Spent a while following internet forum advice given to others with similar problems, but not of it fixed anything.
So anyway the difference between the two computers is that my computer has a newer nvidia graphics card (I forget which version, see PS), and the other computer has an older, nvidia gforce4 card. I guess perhaps the oldness of the card just doesn't jive well with ubuntu.
Interestingly, I actually have a spare of the graphics card my computer uses - which I could theoretically swap into the other computer. However Im not sure its a good idea: the computer it was extracted from had died horribly (burnt out TV card, burning power supply, motherboard damage and a dead hard drive); and the guy who installed the graphics card had done so in a manner which saw its heatsink fan jammed by its own cable. The heatsink had gotten so hot that the plastic guard around the fan had melted. Im just worried that the graphics card may have been responsible for the computers death. Is this likely?

Cheers, RM

PS. Is the a 'hardware manager'-like app in ubuntu, like there is in windows? Id like to be able to look up PCI ids etc of each of the hardware items.

I think it's called lshw-gtk.

the ubuntu pakaged nvidia driver is for the new cards try insatlling the one for older cards from nvidias website

also if you run metacity --replace
as root does everything work fine

OP,after reading this thread pretty fast(so maybe I've missed something) did you ever mentioned PC specifics that you were trying to install that Ubuntu?