How can I determine Memory slot use?

Hi,

I just ordered 2 gigs of memory for my laptop, but I think I made a mistake.*

My laptop (Inspiron 1520) supports 4 Gb of memory, but only has 2 slots.

I was surfing and came across a good dell on a 2 Gb stick so I sort of bought it without even thinking about it.

Now I started thinking...
I don't actually know what the exact memory configuration is inside.
I mean, I do't know if I have 2 x 1 Gb sticks or*a single*2 Gb stick.

If, I only have a single 2 Gb stick inside now, woot! I will have 4 Gb (which was the intention when I bought this thing), but what if I have two 2 Gb sticks in there?

I can't mix a 1 Gb stick with a 2 Gb stick, can I?

Is there a way to tell what the configuration is without opening the case?