I am wondering if the JVC GZ-HD30 has the option to capture in both DV or HD? Right now I am deciding whether a computer is going to be able to handle the High Definition video. If not, I would still like to get the computer, but use it for DV until I get another system for the HD.

I guess capture isn't the right term, how about Recording - can you record in DV mode rather than HDV?

By DV, do you mean Standard Definition?
If so, the answer is no. The GZ-HD30/40 records only in High Definition, however, they do record on either MPEG-2 TS or AVCHD format, allowing a flexible choice for your editing programs & hopefully a bit more freedom with your PC Specs. Recommended Specs are Intel Core Duo 1.66Ghz [or equivalent] with 1GB ram (though I personally suggest at least 2GB)
Most computers meet the basic requirements, however the more juice you have, the better it will run, I suggest get the most powerful PC that’s within your budget :)