The software for the Vyper is available on the Suunto website - its called Dive manager and is free to download. However, I find it less than ideal from a planning point of view. Most people agree that V Planner is pretty good and I would agree, although I use it for planning then dive with the computer (my missus has the Vyper also, I have an old Datamax). The Suunto will give you more stop time than the PC software, so you need more gas than the plan suggests.
V Planner is shareware and a free version is available for the Palm Pilot if you have one of those silly devices. (Just got a freebie cast-off).
Lots of other packages available and no doubt the GUE one will surface. Another free one is Drogon from Gordon Henderson. It too is a good planner but is not yet VPM, but it does some neat little tables if you like that sort of thing...
I've been playing with my Vytec since I got it on Christmas and found the following:
1. Its not built for planning a deco dive. You can run a simulation of a dive but you can't feed it a given depth, mix and bottom time and expect it to spit out a deco schedule. The downloadable software works the same way. From what I've read on various internet sites, this was done on purpose to prevent recreational divers from planning a deco dive.
2. The algorithm in the Suunto's is RGBM. So far, the only software I've found that uses RGBM is made by Abyss and Gap. Both are pretty pricey, about $200.
3. It looks like (and from what I've read) that the algorithm is very conservative. I did a dive plan on the palmvpm program and then tried to run it on the Suunto simulator and it was amazing the difference. The deco obligation under Suunto was almost double that under the PalmVpm program. At the end of the simuation, the Suunto went into error mode.