This may not be the only cause for other readers.
Around late iChat 2 add on Smiley Packs tended to be introduced.
These could cause iChat not to work and not display the Smileys
The cause in this case is that both ends have to have the same Smiley Pack.
Ryan M.'s User Tip on removing and Replacing iChat to "fix" the the issue.
Generic iChat 3, 4 and 5 version of the same info.
There have been reports of the Smiley's folder within iChat getting corrupt but this is really rare and the above reinstall methods will sort it. (Basically there is a .plist file that holds the keystroke listing and it loses the ablitly to match text with pics)
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously