Installing calibre on Lenny is unsupported, It is is very hard because glibc is too old. I once tried to get around it by selective upgrading, and ended up bricking my server.
If you really want to make this go, you can do it using chroot. See http://www.mobileread.com/forums/sho...2&postcount=16
for an example that worked for me. It requires a large amount of *nix sysadmin experience, a server you control, and a fair amount of disk space.