In reply to Rob Exile Ward:
I haven't done any recruiting for a while, but this is what worked best for me:
A really good avenue is word of mouth via your existing staff; good devs tend to know each other.
Recruit locally by preference.
The ones that did best were nearly all self-starters rather than trained up to the eyeballs.
I ask them to describe a project they've done, and then give them one or two examples of things they might work on to see how they would approach it.
Do you need steady but sure, or brilliant and wayward; both have their uses.
Beware of the ambitious ones - you should be able to tell from the cv as well as the interview; best case, they move on after a couple of years, worst case they persuade the rest of your team to come too. I admit this is a bit paranoid, but it happened a couple of times.
I believe Spolsky did well with a whole load of interns, presumably before SO got huge and famous; could be a plan if you're on a budget.
Alternatively, see who in the existing team is prepared to get stuck in.
Just reading your post, I'd say you might need several skill sets possibly not available in one person! Get someone with good web graphic design skills (or contract them in). This really pays dividends. I would look to sticking with the MS toolset as that's what you're familiar with, although of course, there will be many naysayers!
An alternative to web development would be to make the existing app work in a browser; it all depends on what people's expectations of the user interface are. Think about mobile phone support up front, as it's expensive and difficult, and pre-planning is essential.
Finally, look hard at the split of work between the server and the client, if you haven't already done so, as it's likely to be radically different on the web.
Good luck!