As far as I can tell, the power management driver is the low level software that controls the automatic speed switching of the CPU, and other associated functions. I don't think you need it as such.
The video driver may be of use as it allows dual monitor function and may be required to enable the power saving features of the video chipset. However, they do add a few extra processes upon bootup. If you want to still have the power saving (ATI PowerPlay) but would like to minimize the number of processes on startup, I'd install the video driver but not the HydraVision dual display support.
The Battery Maximiser (and Wizard) is useful in that it allows you to monitor battery use very closely and fine tune your power settings. It can also let you see the condition of your battery easily, e.g. the amount of charge left it can still hold, etc. However, if you're mainly interested in the monitoring side and are very keen not to have a big green battery gauge sitting on your task bar (although you can opt to have no icon displayed) you can download MobileMeter instead, which needs no installation. I can't remember where to download this, but search for MobileMeter in the forums if you want it.
I like the Thinkpad Configuration Utility as it allows you to view useful information about your machine and easily enable or disable devices for further power saving. A bonus is that it doesn't auto-load on startup. However, it is about 40 MB or so on your hard drive.
I just fine-tuned my default install a little, and I still have most of the IBM features installed on my R40. I have 38 processes on startup, of which 2 are not standard IBM ones, and I have about 330 MB of free RAM (out of 512) on startup, as reported by the Task Manager.
As for hard drive space usage... well, I just deleted a whole lot of stuff then bought myself a 60 GB Hitachi 5K100
One more thing I should note, that I really love about the default IBM install is that while you see Norton Antivirus, it isn't installed by default. When you run it, it actually launches the installer. Once I realised that, I stopped it, found the installer files and trashed them immediately. Same as with Adobe Acrobat Reader 5.0.
Geoff.
T60P 2007-8JM / T60 1951-A35 / Z60M 2531-E9M / Tablet 1838-23M / Tablet 2 3679-27M
T410 2522-CTO / X301 2776-A17 / X201 3680-FAG / T420 4180-AQ3