wine is an attempt to rewrite all the standard win32 API to run on X-windows (i.e. unix and linux GUI). It's making amazing progress, but still isn't 100% reliable for all windows software.
There do exist free software alternatives for most win32 software - you may want to check out bluefish instead of homesite, the GIMP instead of photoshop, openoffice.org instead of office. AFAIK
there's not a good replacement for Flash. Anyhow, you can read more on wine at:
Don't Stand on your head - you'll get footprints in your hair