Mike,
Before David comes in and bags the netbooks (sorry, David, I'm pre-empting you), I'll put a vote in for a netbook.
You saw me running mine at IISAC. You can get them for around $700 now (if not cheaper through online retailers). Mine has a 9.5 hour battery life. You just can't go past that. It has all the grunt you'll need for imaging/guiding and planetarium software. Don't expect it to be crash hot at processing images, however. I have no doubt, however, that you have a calibrated monitor and system at home for processing, as do many of us.
ASUS eeePC 1000HA (from memory).
Regards,
Humayun