(Brian posted while I was typing this - as he often does
, but I didn't feel like editing it, so here is my entire post)
You shouldn't have to re-create any rooms (make sure you back up your AHX file before upgrading, though).
If you download the "updater" from the link in my signature, it is supposed to update all plugins along with AHP.
I will warn you, however, about SoftStart modules.
Around 2008, X10 redesigned their lamp modules (a category which includes all dimming plug-in modules and wall switches), and added a function called SoftStart. This allows the newer modules to "ramp up" to a desired brightness, instead of always turning on at full brightness, and having to "dim down." The new features are accessed using the X10 "Extended Dim" commands, instead of the older "Percent Dim" commands. Unfortunately, they did not change the model numbers when they changed the design.
The older (pre-2008, non-SoftStart) modules cannot respond to the Extended Dim commands. As a result, Extended Dim commands sent to older modules will result in nothing happening.
In version 3.302, the X10 developers finally added SoftStart functions to AHP. However, since the model numbers of the affected modules didn't change, they decided to default the behavior to the newer SoftStart version, and they created a new category, called "Old Lamps - no Soft Start" for the older modules.
So, here's how it affects you. If you have any of the older (non SoftStart) modules, you won't be able to turn them on using AHP right after you do an upgrade. However, there is a pretty simple fix.
For each of your older (non SoftStart) dimming modules, simply right-click on it in AHP, edit it, and change the module type. Choose the "Old Lamps - no SoftStart" category, and then re-select the correct module type. Once you save and re-download, everything should work fine.
To determine if your modules are SoftStart or not, simply turn them on (using the switch, or a remote - somewhere you can watch them turn on). If the light comes on at full brightness instantly, then it is NOT a SoftStart module, and you'll need to edit it in AHP after upgrading. If it slowly "ramps up" to full brightness over a second or two, then it IS a SoftStart module, and you don't need to change it in AHP.
You should avoid mixing SoftStart and non-SoftStart modules on the same HouseCode/UnitCode combination. AHP gets confused, and might not operate your lights properly.