A friend rebuilt his machine and attempted to install on Win7 64-bit appropriately, but was caught in a loop for GTK2. Expecting this was a typically issue with x64 Ruby, permission etc, I uninstalled Ruby from one of my VMs and attempted to get installed again. I ran into the same issue. After a long while, I was only able to get lich.rbw to run successfully (without asking to install gtk2) by copying the c:\ruby\C:\Ruby200\lib\ruby\gems\2.0.0\cache, gems, and specification folder over to the box I was trying to get working. The only obvious differences I could find were as follows:

Fresh install of gtk2 (manual was attempted as well) uses these versions:
cairo-1.15.2-x86-mingw32
pkg-config-1.1.7

while the working version I have running again is using
cairo-1.14.1-x86-mingw32
pkg-config-1.1.6

I do not know if this is an accurate root cause, but I wanted to share in the event someone runs into a similar problem. I did not find a thread that spoke to this specific situation.