How do i configure QOS on my Linksys WRT54Gv4 using Tomato firmware?

I guess you know the basics, i.e.

Go to QoS>Basic Settings first and enable QoS and set your Bandwidth limits;

Then for to QoS>Classification and create a new rule for each machine, choosing Src IP or Src MAC (depending on how you've configured your Static DHCP), and then fill in the details of the relevant machines and the Classification you want them to have.

Bear in mind that QoS will be most useful for limiting upstream bandwidth, not downstream; this may be still be useful if the other machine are heavy P2P users. Also if you use the basic QoS settings to prioritise things like DNS lookups on port 53 then you may find a noticeable improvement in perceived browsing "speed".

Have a look at these resources, if you've not already done so, I found them useful:

http://www.wi-fiplanet.com/tutorials/article.php/3800416

http://www.decimation.com/markw/2007/10/03/tomato-qos-setup/

EDIT: Forgot to add - the Linksys users' forum also has a section on Tomato, DD-WRT and the other firmwares:
http://www.linksysinfo.org/forums/