Get a Nikon D40
Probably the best bargain DSLR at the moment is the Nikon D40 (about £250 for a body and 18-55mm lens). See this for chapter and verse: http://www.kenrockwell.com/nikon/d40.htm.
Although this is 6MP compared to 10MP for the Pentax, don't make the mistake of thinking that you will notice the difference. Why? - because sensors are rectangular, pixel counts are measurements of AREA but increases in resolution are LINEAR. The D4 gives you images that are 3000x2000 pixels, the Pentax will give you images that are 3872x2592. This is about 30% better resolution, not 66% like the pixel count is meant to make you believe.
@Martin - a) this is an SLR so you look though the taking lens to see what you are about to make an image of - if you are happy looking at a TFT screen or through a little hole, then a compact is fine. b) this is a system camera - you can change lenses. If you got the D40, you would be able to use almost any SLR lens made by Nikon in the last 50 years on it. This means you can choose the right lens for the type of images you are making.
@ Alistair - you're right, movie mode on an SLR is pointless - you can't look through the viewfinder as the mirror will be locked up so really, what's the point?
Mine's the one with a Leica M7 (film) camera in the pocket - still better resolution on 35mm film that digital, even after 18 years since the first one (Kodak DCS100 in 1991) ha ha ha!