Any chance that your laptop is located far enough away from the router so as to get reduced speeds (ie., <15 mb/s)?
BTW, what pc card controller does your laptop use? I'm thinking of getting the pre-n setup, but there is an issue with the Belkin pre-n pc card and O2Micro pc card controllers.
Harvey
[EDIT}
Other possibilities:
1. Zone Alarm 5.x and above are known to cause speed issues - if you use it, try uninstalling.
2. I use Avast as my AV software - there is an issue with the Standard Shield and IE. If you use Avast, try disabling it while you speed test.
3. Other AV products may cause an issue.
Harvey