Hi Parker!
Welcome to the world of photography and this forum. First you will need to decide which brand to go for, as most likely you will be sticking to this brand for a long time as you build up your equipment.
The main 2 contenders are Canon and Nikon, both have their pros and cons and both have a large range of lenses available. There are also others like Sony, Olympus etc who's ranges aren't as extensive. Usually people go for Canon or Nikon.
If you decide on Canon, they offer a few entry-level bodies that may suit you and your budget, in order of ascending price and quality:
1000D - around £380 new with IS kit lens
450D - around £480 new with IS kit lens
550D - around £650 new with IS kit lens
The 1000D is the most basic but is still a very good quality camera, I actually bought one as my first SLR and thoroughly enjoyed it. I did however get it at a very good price with the "IS" kit lens (which they don't come with anymore), but I grew out of it quite quickly. The 450D is a step up from that, but not vastly more expensive and comes with the "IS" (image stabalisation) kit lens which is a decent package. The 550D is a relatively new model and has the latest technology as well as video recording capabilities, if this is of any interest to you. This will be above your specified budget though.
I suggest you read up online on all three of these and decide which one suits you best, if you decide to go for a Canon.
As for Nikon, I'm not completely clued up on the range but from my limited understanding, they offer the D40, D60, D3000 and D5000.....the D90 is out of your budget. Out of these, many have said the D5000 is great and you could get one with the VR kit lens for just under £500. The D3000 also has some good reviews because of the price, around £350 with VR kit lens.
I also recommend you look in the "Classifieds" section of this forum, you can get some very good bargains, especially budget cameras because of people upgrading. I bought a used 40D not long ago for £400 that came with some extras (no lens though but the IS kit lens usually sells for around £60) and that is a much better camera than ones from the xxxD range and will last you a lot longer before you will feel like you want to upgrade. However, since you are a beginner a 40D or 50D may be a bit overkill to start off with.