Here is how I went about installing WP into the ISP account:
1) install WP 3.3.1 in the root of the IP-based account
2) follow the instructions to enable the multisite WP feature.
The key decision to make is whether to build a sub-domain or sub-directory based network. I picked sub-domain.
3) Install the WP Domain-Mapping plugin, enable it, and map the domain names into the network. Use this resource for guidance.
That’s about it.
Oh yeah, one more part was to get 1 pre-existing WP-based blog installed inside the new WP network:
4) Perform a WP blog export and import