I have Slack 14 x86_64. I've installed Truecrypt package from Alien:
Everything works OK, but I don't have AES hardware acceleration. I have Intel Core i5 so it has AES-NI. Also windows version of truecrypt works with AES acceleration.
I have stock Slackware 14 kernel, AES-NI included:
# zcat /proc/config.gz |grep -i aes