I can reiterate what others have said.
1) The capabilities of most DSLRs in the entry range are about the same regardless of manufacturer.
2) Lenses that are suitable for low light are expensive but you can certainly get somewhere if you increase the ISO values (at the expense of noise in the photograph)
3) Flash can help in low light but you should budget about £200 for one that is simple to use (on camera flash is IMHO a gimmick).
I always advise when looking at buying your first SLR you should consider it as an investment in to a system and I suggest looking where you'd like to be in 5 - 10 years and look now at how you would get there.
The final factor to think over is what foggy said about what your friends & family have (if anything) as you can always borrow kit off each other, e.g. you could make a deal where one of you buys a decent flash the other buys a macro lens.
£500 is a good amount and will get you kit that will get good pics I'm sure you can find a D40 with 18-55mm and a 55-200 for that price and you may even find the 55-200 VR (which helps reduce camera shake) for a little over that money.
Almost forgot; also consider secondhand, refurbished or old stock as you can usually find some great bargains - I'm sure you can get a good deal on a Nikon D50 or D70s both of which have better lens compatability than the D40. If you can find either of these with a simple 18-55mm lens for under £300 will leave you with enough left over for a brand spanking new 55-200 VR with IIRC is about £200.
P.S. I only live just down the road in Poynton, so if you fancy popping down for a chat over a beer before you buy - PM me
EDIT- just noticed your age on your profile - offer of beer removed - still happy to chat but will have to be a lemonade if your parents agree
