You can't officially go past 10.7.5 on thet MBP...
I'd highly recommend you go to 3 or 4 GB of RAM no matter what.
You need 10.6 to go any higher, then once at 10.6.8 you can call Apple to purchase a 10.7.5 download, they no longer list it online.
Do you have another Mac that you could enable CD/DVD Sharing on to install it? Any way to Resore the 10.6 DVD to a USB stick?
An Apple Store/appointment might be able to accomplish it.
Alternatively put the other Mac into Target Disk Mode and borrow its DVD drive.
How to use FireWire target disk mode - http://support.apple.com/kb/HT1661 - includes description of hardware and software requirements.
No one mentioned this big caveat about upgrading past 10.6.8:
Lots of software will be incompatible, and needs replacing, or you need to get a copy of 10.6 Server and Parallels to run in virtualization, or to partition your hard disk to keep 10.6 until you can upgrade all the software to be compatible with 10.7 or later.