no need to export anything    just go to  file ~ append then pick the file you want to append from ~  open the materials folder ~  click the mat you want then click append from library

 now that's got it into your blend but it hasn't assigned it to anything, so now go to materials tab and on the little flippy arrows next to name click and you'll see a list of all the mats in that file find the one you just appended and your good to go ......... now I rarely use BI but I think its just the same method but beware of appending a cycles mat to a BI file (or visa versa, think you already got that bit lol )

can you can use link in much the same way BUT if you alter the mat in one file its reflected in other so I'd advise use with caution !!

hope that helps