It should work -- but it does depend on the feature sets and revision levels (and bugs) of your IOS for each router.
Would you suggest purchasing the Cisco IOS versioning manual?
You would suggest upgrading to the 12.0(26) version for the 2505?
Do you happen to know if the 2500 series support PAT?
As well can you show me the link where you are reading this information?
IS this the page?http://www.cisco.com/univercd/cc/td/doc/product/software/