I was about to post a thread requesting help on an issue regarding my girlfriend's new laptop not connecting to my wireless router, but after some more research and tinkering, I figured it out so I thought I would post up my solution instead to hopefully help someone else out in the future.
My girlfriend bought a brand new Dell Studio XPS laptop with Windows 7 Professional. As soon as she powered it on, the wireless adapter was able to detect my wireless network as well as others in the vicinity, but was unable to connect to my wireless network. However, internet and network would work flawlessly if connect via a wired ethernet connection to the router. Also, my old HP Laptop, my gf's work Dell work laptop (both running XP) and my iPod Touch could all connect wirelessly with no problems.
Linksys WRT54GL installed with Tomato 1.27 firmware
Security Settings: WPA/WPA2 Personal with TKIP/AES Encryption
I spent a lot of time doing research trying to find the answer to the problem, and then did some tinkering and found that if I disabled the Security all together (no encryption or passkey), then I was able to connect to the wireless on the laptop. Obviously, I didn't want to leave the network unsecured though.
Things I tried:
Updating firmware on router: I was using Tomato v1.23 and updated to v1.27 - no change
Disabled MacAfee Firewall and Antivirus - no change
Disabling IPV6 protocol on laptop wireless adapter: I would to to the wireless adapter settings and uncheck the box for IPV6 - no change
***Trying different configurations to security settings on the router: I tried different combinations of WPA w/ AES encryption, WPA2 w/ AES encryption, WPA w/ TKIP encryption, WPA2 w/ TKIP encryption, etc. -in the end I left it on the WPA/WPA2 Personal w/ TKIP encryption and this was part of my solution. AES encryption doesn't work with Windows Vista and 7 from what I've read.
Updated time settings on my router: my time zone was incorrect, so I adjusted it. - no change
Disabled Afterburner: -PROBLEM SOLVED!!
After I got the laptop to connect wirelessly, I tinkered around with more settings on my router to pinpoint what exactly was causing the problem. It was a combination of 2 things I changed. The first thing was the security encryption settings. Windows 7 won't recognize the AES encryption, and even if I selected the AES/TKIP setting on the router, the laptop still wouldn't connect. I had to set it to TKIP (only) encryption.
try typing the following into the command prompt to get a little more insight into this.
netsh wlan show all
The second thing thing I did that fixed the problem was disabling Afterburner (aka Speedbooster) in the router settings. I would have never guessed that this would cause problems, and was therefore the last thing I tried but for some reason it needs to be disabled.
I went back and enabled IPV6 on the laptop wireless adapter settings and it works just fine. Also enabled the firewall/antivirus with no problems either.
Hope this helps someone out in the future.