£1000 is a tricky amount for a complete set up, although you can get some decent entry level stuff from the big names. First off, I'd crop 7.1 to 5.1. As long as you have the space to play with positioning, you'll get a perfectly acceptable surround effect, and even in future, I'd rather go for 5.1 with dipole rear speakers than 7.1. with four normal side/rears. Your budget doesn't really allow for a 5.1 set with decent floorstanders, so you'd be looking at the best bookshelf 5.1 set you could get for half your budget, and a decent receiver with the other half. Given you're probably sat at your PC as well, I'd imagine you'd want the stereo pair and center to be on your desk?
For £500 and under, there's options like the older Wharfdale Diamond 10 set (think it's just the sub that's an older model), Mordaunt Short Alumini, Q-Acoustics 2000, Tannoy have a 5.1 at <£500, there's some cheaper Kefs... the list goes on. You'd really need to read up on each of these (AVForums is a good place to start) to give you a better idea of what they sound like, since often preferences when it comes to sound signatures between brands are quite subjective.
Not sure about the receiver (again so many to choose from), but it's important it takes up a good amount of your budget as well, as without good amplification your speakers won't perform to their full potential.
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