I have a website that gets about 20 hits per day. I’m working on promoting the site, and am considering getting to the front page of digg, which could drive tens of thousands of visitors to my site in one day, and my server can’t handle this. I’m wondering if I could move my site over to a dedicated server for a week or two and then move it back, as a solution to my situation.
Is this a viable solution? Does anyone know of other ways to deal with this?
if you are ready to pay for the dedicated server - why not. If you have enough money you will be able to do everything you want
It’s possible, but are you really sure your site will get that big number of visitors?
No one will provide you full dedicated server just for one week. I believe you need to pay for that in full for one month at least
You might be better off looking into cloud hosting actually, you can buy additional bandwidth or resources as and when your site requires them (it’s a sort of Pay as you Go solution). But I agree that you should only consider changing hosts if you REALLY think your site is going to get slammed via heavy truckloads of visitors jumping to your site. The last thing you want to-do is spend all that effort on an occasion which never occurs, that would be embarrassing! 
This is not a viable solution IMO. Most hosts have upgradeable plans and/or contingencies for the same. If your host does not have a clear upgrade path for their plans find and switch to a host that does before promoting the site. Ideally you should be able to upgrade your account by simply paying the difference in cost between the plans. If your’e not on an oversold host this should not be a problem.
Monitor your traffic & upgrade your plan(s) as needed until the same are no longer feasible for a virtual plan, Semi Dedicated, or VPS solution.
Last but not least unless you intend to promote the site using TV, Radio & Printed ads I would not incur the cost of a dedicated server at this juncture. I would use that money to promote the site instead. A VPS or dedicated server needs to be monitored, managed, secured etc. Are you or someone on your team capable of the same? If not you’re going to spend more on the same. Serverpoint is correct a minimum one (1) month commitment are required for a dedicated server.
I suppose if you have 20 hits per day and worrying about digg effect you should be patient. There is nothing to worry about. If you are experiencing Digg effect I suppose you undertstand that those hits are useless and that will not be big loss for you.
I would go for a physical machine either if I should choose a similar solution. Any VPS or cloud hosting service can be scaled and save a lot of money compared to a dedicated server (well at least in most scenarios).
Speak to your current hosting company, explain them your current situation and see what upgrade options they can offer you. If you are thinking about a temporary dedicated server, you may not find a host who will offer a dedicated server for a week or two and the minimum term would be at least month.