According to the Microsoft Website Visual Studio 2008 Pricing there is no need to buy the full product. You can always buy the upgrade for VS2008 Standard or Professional if you have:

• An earlier version of Microsoft Visual Studio
• Any other developer tool (including free developer tools, such as Visual Studio Express Editions or Eclipse)

That looks interesting! So, download the express edition, then you can buy the upgrade version of VS2008!

I just made a copy of the page to be sure, that if MS removes this sentense in the future, I have a copy to witness:
VisualStudio2008Pricing_2008-04-04.xps