Why does my internet connection fail intermittently?
Solution 1:
The university of Berkeley has a website that will analyze all sorts of aspects of your Internet connection such as DNS, ports, upload/download speed etc. It will report anomalies to you. It is here:
http://n1.netalyzr.icsi.berkeley.edu/
Solution 2:
It sounds a lot like a DNS problem, considering downloads do not drop out and it only affects one laptop on the same wirless network.
I would try different DNS servers.
I had a similar problem once and it turned out to be that my ISP's DNS servers were crappy (but that affected everybody on my network).