That number is your (IOMEM) which is partitioned off and reseved for physical resources like buffers, real time logging, etc.
Man, Matt's gonna be proud of me.
Any 12.4 images for c2600 requires an XM series router. typically 32MB flash 128DRAM.
So to answer your question no. You can only use the latest general deployment for 2610's, 12.3(22)
ent 12.4 requires 128mb dram. Altough the 2600's will run 12.4 ip base (thats all) it still does not provide normal features required for most exam topics. such as IEEE 802.1q intervlan routing support. therefore its actually useless as far as study goes.
Actaully i take that back 12.4(16) can utilize vlan trunking with 802.2q if you can get it. it is a 64/16 image.
But ip base lacks IPv6 features. (your call)
For a 2600 i'd stick with 12.3(22) ent basic.
the orginal poster asked about running 12.4 on a Cisco 2610. The IP base image can do IEEE trunking for your intervlan routing. You can run 12.4 ent basic on a 2620 with 32 mb flash, before you say you can't I have. (although with 4-5 subinterfaces on a FE interface it ran out of RAM)
OMG, 12.4 ent basic does not have BGP dont use it.
I don't want this to turn into a debate, but stop hitting the feature navigator to see what Cisco says is supported, vs what actually works (for a lab I'm not worried about running out of memory although in a production network this would be bad).
Since you are running an image designed to run on an XM series router, but I doubt TAC will provide support, (not 100% sure but I've never tried this)