The flight sim community is having a bad year. First the product get canned, and now AVSIM, one of the largest community sites, has been effectively destroyed (we are guessing it was some kind of SQL injection attack). Here’s hoping those guys recover and put the site back up. In the meantime, you can visit the temporary AVSIM forum.
So where can you download FSDSxTweak now? I have made a temporary download here at Skydrive, (with the new FSDSxTweak 2.6 which fixes base material specularity) to Flightsim.Com and other community sites.