The ViCCI testbed is affiliated with PlanetLab. If you already have a PlanetLab account, you can use it on ViCCI. You do not need to register for a new ViCCI account. In other words, a PlanetLab account gives you access to both PlanetLab and ViCCI.
If you do not already have a PlanetLab account, you have two options. One is to first log into PlanetLab and create an account there. You account will be approved if (a) you belong to an site that is a member of the PlanetLab Consortium, and (b) the Principle Investigator (PI) for your site approves your request. Since PlanetLab primarily supports network research, and PIs are typically Computer Scientists that approve accounts for researchers doing network and distributed systems research, this may or may not be appropriate for you. If not, the second option is to create a ViCCI-only account by filling out the following web form.
Note that having a user account is not sufficient for gaining access to ViCCI. You also need to create a slice (project), which will also require PI approval. Once the slice has been created, you will be able to allocate ViCCI resources (some number of VMs) to it. As with user accounts, PlanetLab slices also have access to ViCCI, while ViCCI slices are limited to only ViCCI.