On the regular GOTD page I posted the high registry impact I recorded installing StepShot in win7 32 & 64 bit VMs -- I'd definitely suggest setting a Restore Point in win7 prior to installing & trying it out. From that post: "... couldn't get a figure in win7 32 because the amount was too large & stalled/crashed InstallWatch Pro, while in win7 64 the Regshot2 report stalled/crashed ie9, but I could open the text log [114.5 MB] which says 194859 new keys, 288789 new values [scrolling through the listing didn't see any of the usual temporary keys I've seen when figures have gotten this high in the past]".
Adding StepShot to XP was reasonable for something using Windows Installer, but adding/updating .NET 4 is not a quick task in XP -- again from that post...
Adding .NET 4 to XP Pro SP3... The download [that will be installed from StepShot install] is "dotNetFx40_Client_x86_x64.exe" -- http://goo.gl/2fiu5 -- recorded 774 files added, 39 files modified, 8136 registry entries added, 2496 registry entries modified. Note that the already somewhat slow installs may be slowed further by AV software, e.g. Microsoft Security Essentials was active consuming CPU for much of these .NET & related installs. 1st update was KB2518870 -- http://goo.gl/ZYtwg -- recorded 84 files added, 161 files modified, 548 registry entries added, 212 registry entries modified. Selected at the same time as the 1st update, KB2478663 initially failed, but installed separately afterward -- http://goo.gl/SvP85 -- recorded 70 files added, 164 files modified, 371 registry entries added, 226 registry entries modified. Going to the Microsoft Update site again, another hotfix now showed up as important, KB 2539636 -- http://goo.gl/5qWf6 -- recorded 75 files added, 187 files modified, 1306 registry entries added, 159 registry entries modified. Back at Microsoft Update, 2 .NET 4 hotfixes were listed, but nothing under the important heading this time. The 1st was KB2468871 -- http://goo.gl/QG3z4 -- recorded 78 files added, 181 files modified, 573 registry entries added, 152 registry entries modified. And 2nd, KB 2533523 -- http://goo.gl/Onbap -- recorded 72 new files added, 178 files modified, 602 registry entries added, 152 registry entries modified. Note that if you have Windows auto-update on, it's quite possible that these updates may happen in the background while trying to install &/or 1st run StepShot. Note also that those figures are based on before/after snapshots, & some of the files & registry entries recorded are temporary -- I didn't try to break them down further, intending this more as a rough guide of what you can expect.
Note that there is a tool for removing .NET, but it removes it entirely so you have to start from square one & add all the updates. http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx