iMac 11,2 w/4GB RAM OSX M-Lion install says not enough memory.

I was under the impression I had enough memory to support the new OS. Am I wrong? If not, what can I do?

Specs as follows:

Model Name: iMac

Model Identifier: iMac11,2

Processor Name: Intel Core i3

Processor Speed: 3.06 GHz

Number Of Processors: 1

Total Number Of Cores: 2

L2 Cache (per core): 256 KB

L3 Cache: 4 MB

Memory: 4 GB

Processor Interconnect Speed: 5.86 GT/s

Boot ROM Version: IM112.0057.B00

SMC Version (system): 1.64f5