We build an alike solution interfacing .NET along with Salesforce.com. This can be implemented in two ways. One is to post directly to salesforce.com and other is to proxy the request. Since you are proxying the request, your form doesn't have to match Salesforce.com requirements at all.
You need to collect all the data, then use the .NET HTTP objects compile a post to Salesforce.com with whatever param names they require. You can then call your dropdown "glurm" or whatever you want, as you'll be repackaging the data for sending to Salesforce.com