I'll paste from my last post on this topic. There was an article that went over exactly this in Discover magazine a month or two ago. Summary is that it's harder than you might think.
"You would need more than a garage; you would need a great
garage and a lot of money. And it's not trivial. You need
the oligonucleotides to stitch genes together, and as far
as I know, most companies will check the order if the
sequence represents that of a dangerous virus."
http://discovermagazine.com/2011/oct/21-dawn-of-the-biohacke...Not a great comfort, but companies like DNA 2.0, Invitrogen, etc. have pretty intensive safety checking of what they're synthesizing. No sending off for smallpox.
I'm a college senior, and last spring I and two class teammates were able to re-engineer virus Phi X 174 in only 10 weeks, starting from zero knowledge of genetic engineering. Then we payed DNA 2.0 (a DNA synthesis contractor) to build us the custom virus for only $2k.
Also: on the third day of class, the prof showed us the complete genome of Ebola, and that based on DNA 2.0's price per length, it would only cost $20k to make.