Just take a look here :
www.storm.ca/~ve3iay/spreadsh.html This is a description on how to convert from a spreadsheet to ADIF I had to change the formulas to the Dutch language and find some minor faults, but when you search a little bit it will surely work also for you
http://www.hosenose.com/adif/adif.htmlThis is a discription of the ADIF standard (read it!)
With the informmation from these 2 sites, I've made the conversion. I'm sure you can do it also. Good luck
73 de ON4MGY Nic