im think of gettin git for fs2004...does it have GA traffic too?

WOAI will work in fsx.  As a stand alone simply install it as you would in fs9 only use the fsx option in the installer.  You will loose your fsx airline and boat traffic and the planes won't fly on the correct day of the week (I believe they'll be off by one day) but if that doesn't bother you then everyting else will work.

If you want WOAI to work along side your MTX or fsx default traffic then you'll need to convert the flight plans created with TTools in the WOAI installer to the fsx standard using AIFPC.  AIFPC also ensures that the WOAI flights fly on the correct day of the week and also corrects some changes between fs9 and fsx airports (some airports either ceased operations or changed names).  I use a few WOAI airlines that are currently missing in MTX.