Do you mean manipulate Excel without it being installed on the machine or do you just want a way to do it in .net as opposed to vba?
If you don't mind excel being installed on the machine, then you can use Interop. Here is a sample: DevX.com
As for the other, I'm not 100% sure, I did do a project where I was trying to manipulate newer versions of excel as they are basically compressed XML files but I didn't get very far before we had to pull the plug.
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