On Linksys Wrt54GL, flashing Tomato over OpenWRT 10.03 using the web gui works fine. You need to use the tomato.trx image rather than any bin file. When the router is rebooted, it has IP 192.168.1.1, username=root, password=admin.
Update 2015-07-25: I did this from OpenWrt rescue mode, using command line:
# sysupgrade -v -n tomato.trx
After that, I needed to make a hardware reset: start the router up with the reset button (on the back side) pressed. Keep it pressed for about 15-30 seconds (depending on what source you reead), and then restart (unplug and plug).
Tomato, OpenWRT, DD-WRT and possibly others – any preference and why?
Well, not going to make reviews or complete comparisons of the different possible router firmwares here… maybe a separate post some day.
I started using DD-WRT some years ago (on my WRT54GL). It was a quite nice experience – it looks and feels more like a commercial firmware compared to tomato and OpenWRT. I found it not completely stable though. The latest stable release (v24SP1) is very old (2008) and if you read the forums people recommend to use other officially unstable releases that are supposed to, in practice, be more stable.
This made me try Tomato and OpenWRT.
I think Tomato is based on the original ASUS firmware, while OpenWRT is built from scratch (well, based on or related to NSLU2-Linux, if I remember correctly). This makes Tomato more like a standard router firmware, while OpenWRT looks more like a normal linux system.
There are many rumours indicating that OpenWRT is very tricky to use, and just for Linux geeks. However, I tried 10.03, which has a very nice web GUI, where most things can be customized.
So, for a simple router any of them could work. But Tomato is more practical. If you want more features, Tomato probably has them included and easily available for you.
If you want full flexibility, OpenWRT is the way to go. OpenWRT for example has a repository of packages that you can download and run. Not so useful on a router with just 4MB ROM, probably much better on a 8MB router.
Tomato (like other firmwares) is just an image that is replaced entirely when you upgrade your router. I think Tomato (and most other firmwares) stores all configurations in the first ROM block (perhaps 4096 bytes) while the rest of ROM is read only. OpenWRT has a RO-filesystem with a RW-filesystem mounted on top of it (allowing for changes) – like two partitions. So, upgrading Tomato is essentially trivial (replace all code – keep configuration), but I have not dared to attempt upgrading OpenWRT.
It seems Tomato is more or less replaced by TomatoUSB which supports newer routers (as well as older ones). I have not tried TomatoUSB.
I dont have OpenWRT installed on any router at the moment. If I had a 8MB ROM router with USB port maybe I would try OpenWRT to get a little linux server. However, for that purpose I own (and recommend) a QNAP with standard Debian instead. A bit more expensive, but a much more powerful and flexible solution.
Finally, OpenWRT seems to be 100% GPL/Open source friendly. TomatoUSB also seems to be distributed completely with source code (but I think original Tomato had some proprietary web code). DD-WRT is not open source, and the developer (Brainslayer?) has been critizised for violating GPL. Googling for DD-WRT and GPL controversy should give you much reading.