There are a couple of tricks that you can try to remove the lock that 
IIS/MTS places on dlls so that you don't have to reboot your machine 
everytime you want to test some code.

What I've found is that there are a number of services that need to be 
stopped before the dll is released.

1. Stop the web server - The IIS mmc should have a stop button that stops 
the server
2. Stop the IIS service - use the Services control panel applet
3. Finally I've found there's a service called Protected Storage that also 
needs to be stopped sometimes.

In addition, if the component is running in MTS you will need to unload 
the mtx.exe process that the package is running in. 

It's not that painless a process but it is easier than rebooting.

Alternatively there is a slightly easier way to test components. You can 
actually debug a VB component running in an ASP page or in MTS providing 
you have at least VB6 SP3.