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:
http://www.winehq.com/
HTH
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