I Know there is firmware hacks for the WRT54G. My router is version 3 and my firmware version is v4.20.7. I am looking for a firmware which can let me see other networks in my neighbourhood and I want to be able to connect to them also. Is it possibly to do thos with with a router, or just a wireless network card? This is not for destructive purposes, I don't want to do any harm, this is just for educational purposes.
Educational my posterior. Welcome to the dark side.
What you want is DD-WRT version 23 SP1 01/23/06 at running in client mode. Be sure to read the wiki install instructions before you turn your router into a brick.
it's much easier than the minimal docs show. You go to the: Status -> Wireless -> Survey page. It displays all the available access points in the area. If you click "connect" to any of them, the router magically switches from access point mode to client mode and connects. Putting it back to access point mode is a bit non-obvious, but since you're into education, I'll leave it as an exercise.
However, we're not done with what can be done. The WRT54G can be use as a Kismet sniffer that will show access points, those that don't broadcast their SSID, and clients. Far more than what can be seen with just a site survey. See Kismet and Kismet Drone.
While the Jan 23 and 25 versions fix the DHCP NAK issue, they break the httpd daemon. (Although it fixed httpd memory leaks) When you try to save on the Administration >Management page, the httpd crashes.
The Jan 25 version was supposed to fix the problem which started on the Jan 23 version, but it seems that it didn't.
25.01.2006: [actually includes fixes for both 23 and 25 - there was never a changelog entry for the 23 ]
0000653 DNSMasq as DHCP server NAKs lease renewal request - v23 sp1
0000386 Memoryleak httpd status page
0000589 PPPoE (standard) Connect on demand is broken
0000641 sp1: 13.&16.jan: All "Additional filters" turned ON by default