I think there are thousands of developers that wish for the same thing!
At my company I have to deal with this a LOT as we have some large systems written entirely in Classic ASP, some written entirely in ASP.NET, and some that are hybrid solutions.
Depending on your environment the two can coexist peacefully as long as you don't need to share session state between the two. If you need that, there are a few solutions out there for storing the sessions in a database, but none are very elegant.
Your best bet would be to make a few ASP include files to build a similar look and feel to your Master page, and apply it to your Classic ASP pages until you have the time to rewrite them.
Also, if you have a lot of business logic that you need to share between the two systems, you can take your DLLs and wrap them in COM so your ASP pages can use them too.