DHTML old browser alternative for marquees

[downwitchyobadself]

greetings fellow geeks.

I'm still learning some web dev stuff, and am using some great cross-browser marquee scripts from www.dynamicdrive.com, but what none of them explains is how to get an alternative text to display on an old browser (there are plenty of people on this side of the ocean who aren't up to NS 4 or IE 4 yet, believe it or don't). What I want to happen looks something like this in logical terms:

If (reading browser meets DHTML criteria) then
Run DHTML marquee script
Else
Just show the marquee script as fixed text
End If

Hope someone has an ideer or two...