A 7600GT is a good card indeed. But if you've got the whole £140 to spend, you could probably get an even better card. Though I've never heard of Misco.co.uk before, I haven't heard much of really any UK computer components store. It looks good enough. I've found a couple cards to have a look at, if you want to spend some more money than just the 7600GT.
Those 2 fit into your budget nicely from the looks of it. They're about the same performance-wise. The X1900GT has nearly twice the pixel shader pipelines (36; 20 for the 7900) with a significantly higher clock speed (575MHz vs. 450), but it has 12 texture units as opposed to the 7900GS's 20. So it's really a tradeoff between the two, as everything about the memory is close to the same. I don't know how much the reduction in texture units will really hurt it, but the pixel pipelines will definitely be a big benefit. If I had to guess, I'd say the X1900GT is better, but I wouldn't be too surprised to see the 7900GS with better benchmarks. But then again, you could always stick with the cheaper 7600GT and get good performance in games without having to break the bank. Just one word of advice though: Don't skimp out and get a 7600GS. It's nothing like the GT; it's not bad, but I guarantee it'll be worth the money to upgrade from GS to GT.
And sorry, but I don't have a link for the 7600GT. I wish you luck in finding one.
EDIT: And also, another to consider (if it fits in the price range) is the X1950PRO. I couldn't find one on that site.