As was said by SG, it depends.

Another option that will work is a "converter". Some inverters do not use a sign wave and some equipment can not use the modified sign wave the small inverters put out.

A converter steps up the 12 +/- volts to what your computer uses without the loss an inverter has. You can see a sample of a few at;
http://www.powerstream.com/ADC-p006.htm

I have NOT used the company in the link, so can't speak for them. Just giving an example.

Greg