I was wondering if it is ok to hook up a preamp to a computer for use with impulses, without connecting it to a power amp and cab or will I need a load of somekind not to ruin the preamp?
If it is just a preamp you don't need a load. Poweramps and heads DO need a load.
This is true. It's the power section that's the issue here.
However, you can run a head on standby without a load. Just don't take it off standby...
But some amps won't produce any sound at all on standby.
I have used Rocktron Piranha, Peavey Rockmaster and Sansamp PSA-1 like this.
Which of that three preamps you like most???