Hi Chris,
The largest PCMCIA flash card size that should be supported on the 3660s is 20 MB. They are considered linear flash cards (as opposed to ATA flash disks which you will see on some other router platforms). However, using the internal flash SIMMs, you can upgrade a 3660 to support 64 MB flash memory.
If you are looking for additional flash to store larger IOS images, I would recommend purchasing internal flash SIMMs. There are two slots for internal flash memory on a 3660 -- you probably have two 16 MB ones installed now, if your routers have 32 MB flash total. Look for some 32 MB SIMMs (the part number should be MEM3600-32FS) for each router. The SIMMs can be different sizes, so if you only need 48 MB flash you can replace one of your 16 MB SIMMs with a 32 MB one and have a total of 48 MB. If you need 64 MB, then replace both 16 MB SIMMs with two 32 MB ones.
Here's a document for you on replacing memory on the 3600s:
http://www.cisco.com/en/US/docs/routers/access/3600/hardware/notes/3636mem.html
Hope this helps,
Chris
