<p>I've been contacted to see about updating an old legacy web application that was built using ASP and Access. The server is running Windows 2000 Advanced Server and I believe IIS 5.0 (I am trying to get confirmation on that, but the company isn't technical so I highly doubt Apache is running on the server).</p>

<p>What languages would be viable for updating this web app on the above platform? I've never touched classic ASP much less done any web development work against Windows 2000/IIS 5. There are no plans on updating the server to anything new due to budget concerns.</p>

<p>I'm leaning at the moment to moving to an SQLite-based database (customer isn't too keen on installing MySQL at the moment but I'm still in planning stages and this is a relatively low-traffic website) but what language would I pair with that? Does ASP.NET work well under IIS 5? Does PHP perform worth anything under this kind of setup?</p>

If the company is concerned with cost, I would be very conservative making changes.  Concentrate on why they want to update- do they want to add new functionality?  What are their mid-to-long term plans for the site?  Are they having trouble maintaining the site?  Going to a custom .NET solution may only complicate things further unless they are willing to make some ongoing investment in development.
If it's a relatively simple site, they may want to consider a platform like DotNetNuke.  There are hosts out there that sell ready-to-configure sites that can do quite a lot with a minimum of configuration.  That combined with a profressionally developed DotNetNuke UI template (TemplateMonster.com offers them) may be a good solution.
If they do want to go with a custom solution, ASP.NET runs fine on IIS 5.0.  I believe you can run the .NET Framework up to at least 2.0, not sure about 3.0 or 3.5.  Language won't make a difference to functionality, so C# or VB.NET are fine, all things being equal.