As a developer of approximately the same vintage, I'd say the most natural transition is to C# and full .NET skills. Add to that SQL Server skills for good measure. Most of your ASP skills will translate naturally and you can take advantage of Microsoft's free C#/VB.Net Express compilers and SQL Server Express.

Also, I'd highly recommend you invest in a Microsoft Certified Software Developer (MCSD) certification. Get one of the study guides and take the exam. It'll only cost you $200-$300 total but will give you proof that your skills are verifiably current in an interview.