Minimum specs for internet TV?

Hi all

I'm looking for a small PC to connect to my TV (it has a PC monitor socket) so that I can watch online TV, BBC iPlayer etc. on the TV instead of sitting in front of the PC.

I've seen some cheap PCs on Ebay but would like to know what the lowest specs for such a PC should be before I buy anything. Having just spent a load of money on the TV I don't want to spend to much on a PC.

I've seen a lot of small Dell PCs, some don't come with an OS, could I use Ubuntu on something like that to watch TV?

Thanks in advance.