I also need LHA, but for Linux. Alas I apparently don't have it, and it's not on Debian's package list, as far as I can tell...
make sure your /etc/apt/sources.list deb line has "non-free"
In my unstable I have
deb http://ftp.fi.debian.org/debian/ unstable main contrib non-free
After you've added the non-free part,
apt-get update and
apt-get install lha.
Package: lha
Priority: optional
Section: non-free/utils
Installed-Size: 176
Maintainer: GOTO Masanori
Architecture: powerpc
Version: 1.14i-10
Depends: libc6 (>= 2.3.2.ds1-4)
Filename: pool/non-free/l/lha/lha_1.14i-10_powerpc.deb
Size: 63008
MD5sum: 2cf0aa31c2eaf10015d0bb0d1e74c674
Description: lzh archiver
The famous lzh archiver, known from DOS. When mixing DOS and Unix you might need it. (Especially for fido <--> rfc conversions.)
Tag: interface::commandline, role::sw:utility, use::storing, works-with::archive