a less aggressive route might be to SHIFT delete all in 'My Documents' - assuming thats where you ket all your sensitive stuff, (permanently dleting this) then doing a disc optimisation, which pulls all the bits of those files that are supposed to still exist and puts them in contiguous sectors. Very little likelihood of anyone finding anything useful then.
Assuming you also wipe your document history and Internet browsing history, you might then choose to system restore.
And you could then flog it !!! (I'd risk it after that anyway)