The answer is no the SDK is not limited to 64 bit OS's. I have now succcessfully installed it on my Windows 7 32 bit machine. My problem was a corrupted download.
Update: Even though the SDK installed it was a bit pointless given that it didn't contain the libraries necessary to build a SharePoint client app. However looking at the sample code in the SDK was useful and I then copied the required libraries from my SharePoint server to my client and was able to reference, build and use them. The Client object model looks like a bit of an oddity to use but even though I've only been working with SharePoint for two days I'm not suprised, still I think it will be better than manually extracting data from XML elements.
ClientContext context = new ClientContext("http://wdev2008:22880");
List sharedDocsList = context.Web.Lists.GetByTitle("Shared Documents");