Hmmm, probably not a particularly useful response... but I'll throw it in anyways...
If you stick to basic CSS, and ensure that you use valid code and a correct DocType, you should get near to 95% compatibility for different Browsers and OS.
I only test on Windows IE6, MFF 1.1+ and NN6 (orNN7!).
If I can get it right in NN, it seems to work on most other platforms/browsers.
Once you leave the path os "standard", you start hitting major problems.
So don't!
You'd be amazed what happens if you applypadding to a parent instead of margins to a child!
Applying display:block to Span or to flaoted elements helps keep IE in shape, as does using vertical-align: // line-height // height-width etc.
And avoid Hacks (so many people are now facing the problem of MS actually fixing bugs with IE7, so half the sites are now Knacked!!!).
I am serious too, simple, basic coding and styling can work wonders... as will expanding you hands on knowledge of Floats, Absolute, Relative and Default behaviours whilst creating content flow!
Leave the programs behind... I can manually design, cut up and create a page design in 24 Hours... and it will work on most if not all browsers... don't rely on software - use your brain and common sense, more reliable, and you should normally carry it with you

(apart from Wednesdays, when I leave mine at the Cleaners

)
Push comes to shove....
CSS Discuss
A List apart
HTML Dog
Position is Everything
Mandarin Design
...
I will also add "SitePoint"... just don't take "Everything" as gospel.
Well, good luck