Reason for edit: Missed the laptop thing 1st time around. May not apply:

Had a similar problem with my PC, 256MB ram on a AMD @ 1.6, with a decent Radeon card with 32MB (older card though). A 5700Ultra fixed the problem (128MB vid ram). Can now run the complex sites at 1024x768+ with no hesitation and decent frame rates. Do what these guys suggested, make sure you've got the latest sound & vid drivers and divx is up to snuff, but the 32MB vid ram may be the issue, and your just seeing a temporary lag when it has to load new maps to the card.