Some have claimed success with the MegaRAID card following [link|http://www.ale.org/archive/ale/ale-2004-02/msg00450.html|this] recipe - installing SuSE 8.1. (The thread is about trying to get RedHat 9 running on a box similar to yours.)
You can find it here:
[link|ftp://ftp.suse.com/pub/suse/discontinued/i386/|ftp://ftp.suse.com/p...iscontinued/i386/]
(They have a Live CD and install versions.)
The stuff I've seen about the 3c90x has been rather nasty. Greg is probably the person to help there, but SuSE might work out of the box with it (it looks like [link|http://www.jaschke-net.de/Dell-Inspiron-4100.html|it does]).
I know, you want to run Debian. However, getting any flavor of Linux up and running on it might make it easier to figure out what needs to be done to make Sarge happy.
HTH. Luck!
Cheers,
Scott.