You'll have to find out if someone installed TouchFreeze or similar. I can't guess what they installed.
When I type on my keyboard, the touchpad disables itself, like the "Hide Pointer While Typing" option avaliable for Mouse properties. This is very annoying when for example playing games, but also when tying and you want to quickly want to move the mouse after tying. This is because the lock-up lasts for about 1 second after typing.
I have tried disabling "Hide Pointer While Typing" option, and there is no option in the Synaptics specific driver that I can find.
I run Windows 7 Home Premium 32-bit, but I had the same problem in Windows Vista Home Premium 32-bit.
The laptop is an Acer Aspire 5935G.