<p>I know we are <em>really</em> behind the times here, but we are just about to upgrade from .NET 1.1 to .NET 2.0.  </p>

<p>Thank you for your sympathy.  </p>

<p>Anyhow,  are there any gotchas we should look out for?<br>
Do you have any general advice before we jump in?  </p>

<p>Please do not post telling me to go straight to 3.5:  2.0 is all we're allowed!  </p>

<p>We're using mostly C#.  </p>

Yes.  The most important thing for you to know is to use a Web Application Project, not a Web Site.  Web Sites use a totally different compilation model and migration is pretty much a disaster.  Web Application Projects are much more similar to how things worked in 1.1.
We also had an intermittent problem with redirecting from the login screen, but according to Google, we were basically the only ones who had that problem - we've since resolved it.
Most of the other problems we ran into were small and easy to navigate, and the overall experience was a net improvement.