Yes. You can do it the traditional ip/mask way:
192.168.0.1/24 (only people coming from 192.168.0.1 through 192.168.0.255)
or by using hostnames comma.
foo.com (only people coming from foo.org)
It's also possible to combine several ranges and/or hostnames using comma:
192.168.0.1/24,10.0.0.0/8,foo.com
For more information:
http://download.pureftpd.org/pub/pure-ftpd/doc/README.Virtual-Users
If you're not familiar with ip/mask, see wikipedia:
http://en.wikipedia.org/wiki/Subnetwork
-Isak