Just....biking?

There's this rumor going around that I might have bought myself a road bike. If said rumor turns out to be true, I will likely want to ride said road bike. Problem is, I'm on a running jag that isn't going to end until, um, late June. 2010. At the top of Mt. Washington.

So, my question is, will I build any decent bike fitness just, *gasp* toodling around? I was thinking of doing drills and building distance and, you know, "training," but I really don't want to mess with my run program. I'm thinking I will use the bike more as off-day or cross-training stuff. And hopefully commute to work at least some of the time (17 mi one-way, but I'll drive partway there until I build up to that). Will that allow for active recovery, or am I setting myself up to push too hard? I'm rebuilding my run after a long hiatus, so I don't want to screw it up. If I do just go out and cruise around for 30-40 minutes a couple times a week for the next year, does it seem pretty likely that I'll be able to jump on a real program and train up for a longer ride in a pretty short amount of time?