I had a very similar problem. my solution was;
1, Down grade to Windows Vista.
2, Change my Router from the LINKSYS WAG160N back to the original SKY Netgear one.
3, Use Static IP addresses.
Now my laptop works fine again except that it's not Windows 7 any more.
Apparently Compaq say I'm entitled to a free upgrade to Windows 7, free except for the £21.99 postage. How heavy is it? I just sent a parcel that weighed 12.7kg and it only cost £14.