MUI isn't a replacement icon set, however you still need it to run a lot of programs so go ahead and put that on there, along with MagicWB . The only other choices beyond that (NewIcons, GlowIcons, Ken's Icons, etc.) require a more souped up system.
Also don't forget Peter K.'s icon.library! 
actually on the topic of icons ive added some nice ones to my setup of basic newicons ..found a 030 chip icon for my system drive..wanted to use the cd32 icon i saw on my games drive .. ..cant find it anywhere ..anyone else seen it??
