Dataming Of Subsets Question

Have not found an active general data mining forum yet so asking here.

I'm new to data mining band have been given the task of setting up a data mining system. The problem is that our setup seems pretty non standard and I'm not sure how to use data mining on it or what my expectations should be. The situation is:

We have a large and growing set of strings which we get requests for (> 100,000). The requests have many, mostly nominal (non-numeric), variables associated with them. We can only handle a subset (probably less than 10,000) or the strings at any one time. We want to use data mining to analyze historic requests so we can figure out which strings we are going to handle under a given set of variables. So given that our variable currently have values X1, ..., Xn, what subset should be use given than a large database of historic string requests.

Anyone know what techniques would work well for this kind of problem? This is a quick and dirty kind of project, no special purpose hardware or expensive software on this one. I've been looking at using rapid miner but not sure that it's a great tool in this case.

thanks in advance,
max