I'm afraid that with that budget you cannot afford a digital SLR. Not even with twice the budget! So this puts you in the situation of having to just upgrade what you have...
Let me begin by saying that I don't shot digital. So... what am I doing giving advices here!!!??? Well, the reason is that I've been doing some research lately to buy a digital myself (just as company to the film, not to substitute it!!), so I've gone to quite a lot of literature on the possibilities available and...
...and I should be able to have an opinion, after all!
I would encourage you to go for a "prosumer" digital. You already have a Point&Shot, and if you're planning to keep it, it would be silly to have a new one that will offer you practically tha same, wouldn't be?
These "prosumer" give you the same possibilities as the one you have, but they also will let you decide a lot of things, almost as with a DSLR. It's a more affordable way to have the decisions in your fingers while using a digital.
Someone will probably tell you that you should save a little longer and go for a DSLR. Mmmm, that probably would be a good advice.
Take a look at this discussion for some thoughts:
http://www.thephotoforum.com/forum/showthread.php?t=20690