8 speed cassette on a 7 speed DA 7400 hub - possible?

Thanks gents. I'll stick some photos up when they arrive - hopefully this weekend.

the issue surrounds the fact that the STI shifters are 8 speed. Will these work freely on a 7 speed cassette? Other option is to try and swap them with someone here for 7 speed ones....

Your comments are greatly appreciated tho!

Not as stock no.

The distance between cogs differs between 7 and 8 speed. As Rodabod says though, you could respace the 7 cogs with 8 speed spacers and then just not use one of the clicks on the shifter. An 8speed cassette will cost ypu a lot less than an 8speed STI, infact you could probably pick one up for free if it's got worn out cogs and just salvage the spacers from it.