|It's the same as flashing a BIOS on a motherboard, if there were a power failure in the middle of writing an update to a motherboard BIOS, the motherboard is usually toast unless you send it back to the factory or the BIOS chip is removeable and you get a good chip from the factory. If you have the proper special equipment you can restore a bad BIOS or firmware problem, but most of us don't have the specialized equipment to do that, so we can't just "try again".|
Wireless routers usually are upgraded using the firmware on them. They have a web interface which you access through a browser. Within the web interface is a dialogue to upgrade the firmware. You have to be using the proper browser (or one that's compleatly compatible) and you just select to upgrade and the dialogue request the file to use. You point it to the file (just like uploading a file to the Internet) and it spends a minute or two rewriting the firmware in it's flash ram. If something happens while it's in the middle of re-writing it's firmware, or if the file itself is corrupted or incorrect in some way, the firmware in the flash ram becomes corrupted and will no longer boot the router. So, you no longer have a web interface to access. There's no way to communicate to the router unless you have the special equipment and interface software to "push" a new firmware correctly onto the flash ram.
The WRT54G is the original wireless router that DD-WRT was developed on (hence the name). One thing you can do is go to the linksys support page and download the latest firmware update for your model and carefully follow the linksys instructions for upgrading your firmware. That way, if it doesn't work out you can write to the linksys support and ask them to help you. After you've experienced upgrading the firmware using the factory firmware, then you can try using a 3rd party like DD-WRT, OpenWRT, whatever...
There's a pretty good overview of DD-WRT on wikipedia:
and at the bottom are links for more information about other 3rd party firmwares. The situation is, none of these freely available open source firmwares are going to be simple to use. That's intentional. If you read the FAQs and stuff, you will see that they ARE NOT wanting to encourage people who don't really know what they are doing from trying to do this. The people using their own time and efforts with no monetary compensation DO NOT want to hear from people, who didn't really spend any time or effort in learning what they are doing, complaining, "i tryed ur sofware an now my router don't work. what u gonna do about it. waaaa". If you want to do this for free, you are on your own. Otherwise, pay somebody to do it for you.
A Linksys WRT54G was the first router I did this with. I took the time and carefully identified the model and all other reference numbers. Then I read comments on forums from people who had done it on the same model,version,etc as I had and then downloaded the exact file they reported using and then just did the upgrade just like I'd done the Linksys upgrade. And it worked great. No problems. The router just booted up to this DD-WRT and then had all sorts of capabilities and configurations which the orginal Linksys firmware does not have. But, I was never totally confident that it was going to work until it did.