The new low quality stream on the tvcatchup.com website works fine on N900, but I've updated the script anyway because it gives a little bit better picture quality. The new script uses the built-in browser, so Firefox is no longer needed. (The browser opens the playlist in Media Player, but the script kills it brutally.)

The main bottleneck is the decoder, which uses a lot of CPU, so make sure that you don't have any programs running in the background. Mplayer has lots of command line options which can be used to reduce the CPU load at the expense of lower picture quality, so you may also want to experiment with them if you find that it runs too slow.