The CPU can be OCed but the Motherboard bios probably dont allow it.
Most PC manufacturers dont offer any options in the bios to overclock so that people buying them dont cook their PC and try to replace it under warranty.
The only way to OC the CPU is to purchase another Motherboard.
Asus P5N-D 750ihttp://www.newegg.com/Product/Product.aspx?Item=N82E16813131232
ASUS P5N-T 780ihttp://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3536897&CatId=3495
You need to make sure that your case will fit an ATX motherboard and that there are no proprietary connections that are Lenovo specific.
Why are you wanting to OC?