If Artrage crashes on Windows it also attempts to save out a backup copy of the document ( ARRestart.ptg ) to its Application data folder.
This is located here: C:\Documents and Settings\<your user name>\Application Data\Ambient Design\ArtRage 2\
So, I'd recommend checking there to see if that file exists and whether it can be loaded.
Otherwise, you can email your painting to me at firstname.lastname@example.org and we'll take a look at it for you to see what can be recovered. If the painting is larger than 10 MB, let me know and I'll send you some instructions to get it to us another way.