Assuming that it is the same as what I found here:
http://shop.lenovo.com/ISS_Static/merchandising/US/PDFs/K100_tech_specs.pdf
the most it will do would be the fastest C2Quad you can find. Something like this (except that they are out of stock):
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115130
Looking at other boards with the same chipset as what I found in the first link it 'should' take the C2Quads. Now as to if the bios will do anything with it or not is annother matter, and I would contact Lenovo to see if it will work.
If it will then you should expect a huge speed increase (one of the few times I would reccomend a CPU upgrade in fact):
http://www.anandtech.com/bench/Product/70?vs=49
Still not going to get you into the modern era of core i5 and i7, but you can expect a 2-3x increase in performance compared to where you are at now, and if that is enough then it would be a good investment.