to install this module simply follow the canonical procedure
for installing any perl module
$ tar zxvf Apache-SizeLimit-0.XX.tar.gz
$ cd Apache-SizeLimit-0.XX
$ perl Makefile.PL
For static mod_perl use -httpd /path/to/httpd
For dynamic mod_perl use -apxs /path/to/apxs
$ make
$ sudo make install
for further directions, see the README.