It depends on your situation. You can indeed install VS 2010 B2. You can target to the 2.0, 3.0, 3.5 and 4.0 .net framework (although the 4.0 is not supported yet in production environments). So if you want you can use VS 2010 B2 and target to the 3.5 framework to make full use of the new C# improvements and then upgrade to VS 2010 RTM when it arrives.
Another scenario you can follow is to make use of VS 2008 and upgrade to VS 2010 when it hits RTM. So it is up to you....
Ewald - Please remember to mark the replies as answers if they help.

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