IPhone Simulator locks up immediately upon Build / Run

I'm having a problem getting my **MacBook** set up to build **iPhone** **apps** in **xCode**. The iPhone **Simulator locks up** and shows the "spinning circle" busy icon.

I've tried everything I can think of, including

- resetting the simulator
- tried all of the different hardware options in the Simulator (5 or 6)
- tried the two debug build choices in xCode.
- uninstalling the SDK and completely reinstalling
- tried creating xCode projects on Desktop and in \Developer...

I downloaded the SDK "**xcode_3.2.2**_and_iphone_**sdk_3.2**_final"

I'm just upgraded from Leopard to **Snow Leopard (10.6.3)**. I've run all the software updates. **xCode** version says **3.2.2** (1650)

If it matters, my MacBook is 3-4 years old, 13 inch, dual 2.16 ghz intel cores, 2 gig RAM. I've never had a single problem with it.

I would be so grateful if anyone can help me

thanks so much,