Cautious fellow that I am, I'd grab the helpdesk job and hold on tight. The other gig sounds better, but also awfully speculative. What if it falls through? Day-to-day survival is the first priority. I say see if you can schedule the contracting interviews around the job you actually have.

Second to the above consideration, I'd never turn down an opportunity for new training and experience. But if you really want to get ahead, you might want to pursue training apart from either of these jobs. Whatever you can get on the job, take it, but don't settle for it. There's lots of stuff that you can teach yourself at home, if your spouse is sufficiently understanding. There are certifications you can pursue in your spare time, unless of course you're trying to work two full-time jobs. Maybe do a small open source project just for bragging rights.

Stuff like help desk and Visual Basic are things I'd look at as strictly temp jobs. A way to get through the current crisis. But long term, you need a broad range of skills. And these days, working close to the hardware is good. There are military contracts using COTS technology, and some of that hardware needs software. You don't even need to enlist.