I don't see that option either. This has been my biggest disappointment with gmail for Android. Before, I had a Blackberry and assumed this was just a limitation of the BB gmail client (it pretty much sucked). While the Android client is much nicer, there is still no way to select text that I can find.
OP: Does the Fascinate have a hard keyboard? I only ask as my Moto Droid running eclair was able to copy text by sliding it open and holding down the shift key with one hand, and highlighting text with the other. If you've got a hard keyboard, it may work for you as well.