The Apple company store won't sell you upgrade RAM and either
Crucial or
Other World Computing is a lot less expensive, and far more reliable than any other sources for Mac compatible memory.
The last time this subject came up (and just now, too) I looked at Crucial's website and found that they've apparently undergone a change in policy and no longer sell RAM upgrades that surpass Apple's specs.
The 4GB DIMM I purchased from them to upgrade my MacBook to 6GB is no longer available:
Your null [sic] MacBook (13-inch, Early 2009)
system specs as shipped
memory
Maximum memory: 4096MB
Slots:2 (2 banks of 1)
*Not to exceed manufacturer supported memory. (Emphasis added)
OWC sells the upgrade:
Upgrade options for
White MacBook 13.3" Intel Core 2 Duo 2.13GHz
Apple factory specification maximum 4.0GB,
OWC tested to support 6.0GB maximum RAM.
Works with Model Identifiers: MacBook5,2
Time for some e-mailing, I guess...more to come.
Edit: OWC sells the upgrade to 6GB in which Bob_00001 would be interested; Crucial does not.