Usually with DBG installed, Jasper appears right after the Imoen rescue scene and the first auto-save(Irenicus is still Old School; to get rid of Irenicus Scenes, you need "Shorter Cutscenes" from BG2 Tweak Pack, available at gibberlings3.net).
"Before and after the FixPack" is a Very Bad Thing. Installing Baldurdash after mods(including DBG) is a big no-no. If you really did that, do a full reinstall. Install Baldurdash(if you must install Baldurdash instead of BG2 Fixpack from gibberlings3.com) right after the patch, install the patch after the game, and install the mods after all that.
Barring that, here's the usual advice:
Check your Weidu.log in your BG2 directory; check that DBG is there. Also, make sure to check the quick reinstall/clean backup topic
http://forums.pocketplane.net/index.php/topic,17555.0 - saves time for all your subsequent reinstalls. Make sure the game and other game-related utilities are not running as you install the mod.