Read this thread, get an idea of other issues with these cars, Legacy GT common issues
Here's some useful links...
I found this video EXTREMELY helpful.
CovertRussian's Up-Pipe install
Infamous Up Pipe Install - M Sprank
I found that I had to jack the engine up in order to get the OEM up pipe out. My dad's friend Mike, who did an up pipe install on his earlier model WRX had to do the same. When/If you jack up the engine, make sure you jack it up by the oil pan, with a block of wood separating the oil pan from the jack so you don't puncture the oil pan. This isn't a hard job, but it isn't easy either, so take your time, take deep breaths, and make sure you use all new gaskets.
Your OEM gaskets are nearing 10 years old, they're shot, don't reuse them; it's not worth a pre-turbo exhaust leak considering how much of a pain in the butt this whole process can turn out to be.
Because my exhaust bolts were rotted on all the way to the tips, I ended up having to drop the down pipe, and the entire exhaust system along with it. I did not have to remove the crossover pipe, but I did have to remove the passenger header, and you will too.
And MrTris, I don't think dogs spool. Though I could be wrong, i've been wrong in the past.