i've only used virtual dj a few times, but as most popular dj programs are very similar, take it form me: mixing with a laptop is so easy it's ridiculous, basically all you have to do is match the BPM of familiar songs (or unfamiliar as you get better) and learn to utilize the levels and effects as you go along. most house music hovers around 120-130 BPM so house is a good genre to get started on.
i've never bothered to try, but i imagine mixing without a controller would be a bitch, so here's some entry-level equipment to get started with:
http://www.amazon.com/Numark-Total-Control-Software-Controller/dp/B000QS76QC/ref=sr_1_4?ie=UTF8&qid=1325641724&sr=8-4
and
http://www.amazon.com/Numark-DJ-Multi-Channel-Interface/dp/B000S5Q2EK/ref=sr_1_7?ie=UTF8&qid=1325641724&sr=8-7
these are very expensive separately but there's a boxed set that also comes with headphones that i got new for around $120 on amazon. look around the internets, you'll probably find it for a similar price.
i had it easy since i was friends with a bunch of local DJs and caught on really fast with their help. so if there's a local DJ that does small shows and isn't a dick, watch him play and ask for advice.
just spend some time with it, you're not gonna be ready to DJ a house party or whatever right off the bat, but you'll be surprised how quickly you'll learn if you stick with it.