Softsynths comes in VST or other plug-in formats. So the idea is the same - if you use lots of plug-ins, your CPU will be taxed. Effects are also plugins.
But with 2GHz, you should be able to get around with most things. I don't see a big problem at all. Also remember that plugin softsynths (VST or otherwise) come in different shape and sizes - some will tax the CPU more than others.
The main thing is that your PC MUST be dedicated to only using music software and optimised. If you use IE, Microsoft Office, games etc with it, it wouldn't work. With all these removed and running ONLY music applications, your machine can handle more than you think - DAW-wise. And as we have discussed this extensively in many previous threads, you don't have to get a new PC to get your PC dedicated to music software. You can dual boot your current PC.