are you planning to do this on the client or the server side ?
http://www.greggriffiths.org/webdev/both/excel/ covers some of the options that you could use, your best bet may be the Office Automation via ActiveX, although the examples on the site are geared to Excel and the automation being done on the client side, the code would still work, after some slight amendment, to run on the server side if you need it to.