VB limit itself to X CPU usage and ram usage

Open your project properties page, then select the compile tab
Click on Advanced Compile Options, you can select the Target CPU there

In .NET 2008 you can also choose the framework
I dont know how you can limit the RAM usage though

I am not sure why you want to do this, however, for CPU usage, have a look at Processor Affinity settings http://msdn.microsoft.com/en-us/library/system.diagnostics.process.processoraffinity%28v=VS.90%29.aspx

Am not sure if you can do this for RAM

You may want to look at http://blogs.msdn.com/b/oldnewthing/archive/2005/03/21/399688.aspx which discusses various insights into what you are attempting to do (though mainly discourages it... almost)

I have had to do this,
I had to set the Target CPU to x86 so when it was run on a 64 bit OS the underlying 32bit only DLL would work, without doing this the DLL failed to work

Only setting a RAM usage maximum for an application will only prevent a crashing application from using all the RAM of the machine and the application will be terminated with an OutOfMemory exception. If you want to stay below a defined limit and keep your application running, the application itself has to handle things like caching of data in a way that it uses not more than a defined value and swap not frequentyl used data to a temporary file.

What is the best way of setting a RAM usage maximum for an application? (in VB.net)

That is right, it seams it can not be done. Thanks anway.