Hello,
Right now I have a Sony point and shoot, I think it's 8.1 MP. It's a good digital camera for bringing to parties and whatnot but I want to get into DLSR cameras. I have about $300 to spend as of right now and ~$75 more if I sell the point and shoot. (WTF I just Amazon searched it (DSC W 150) and it's +$300 in the color I have.) I don't remember spending that much on it... Whatever...
First choose the brand. Nikon or Canon. It will be expensive to switch later so plan ahead five or more years. Look at the lenses and so on from each company.
So, let's say you like Nikon. The best $300 deal will be a used D50 with the "kit" 18-55mm lens. Pretty easy to find one of these for $300. Later you can buy another lens and so day later another body.
You will get the most bang per buck with used gear untill you have about twice or 3X your current budget