The main difference is the jump in megapixels from 10.2 to 12.4 MP, HD video mode and faster burst rate. There's also a higher ISO range (up to 12800 as opposed to 6400) and 11-point focus system instead of 5. Essentially the K-x sits between the K-7 and K-m, being based around the same body as the latter but carrying a few more semi-pro features. Both are cracking DSLRs though, and the K-m would be superb for a beginner. Image quality is fantastic as well.
Picked up a KM, twin lens kit plus extras for just under £300. Its virually new and still in orign packageing.
I've always had olympus compacts until now but it seems good and cheap enoguh for me to justify.
Takes AA batteries thou which i'm not too sure about at the min.
Looking forward to getting to grips with everything.