Re: Beginner - Which DSLR should I get?
For a £300 (ish) budget, your choice of new cameras is limited to the entry-level model (& kit lens) from each manufacturer - i.e.
Nikon D3000 + Lens Kit (18-55mm VR)
Canon EOS 1000D + Lens Kit (EF-S 18-55mm)
Olympus E-450 + Lens Kit (14-42mm)
Sony Alpha A230 + Lens Kit (18-55mm)
All the above are available for under £350 if you shop around - Currys have the best prices on the Nikon & Canon at the moment. There's also Pentax, but their entry level K-x + 18-55mm kit lens would be stretching your budget to around £380
Any of the cameras listed above would be capable of good results in the right hands, but be aware that when you buy a DSLR, you're buying into a system; so when deciding on a brand, you need to consider it as a long-term (possibly lifetime) commitment.
As the features and capabilities of cameras in any particular price band are so similar, you should base your choice on handling - i.e. what feels the most comfortable, if the controls fall readily under your fingers and if the menu interface makes sense; so get to a good dealer and handle all the models you're interested in - and don't be swayed by sales talk - your instinct for what feels right for you is your best guide.
As for second-hand, there are some good cameras to be had at reasonable prices if you choose carefully, but I would advise against buying something just because it's a bargain, as it may not be the best camera for you.