Whilst I agree vista isnt the best thing to come out of Redmond how do you know its that which is "slowing" it down .
7 may slow it down even more depending on the spec of the laptop and the operating system setup.
You may have a slow processor and a small amount of memory a low spec graphics card and even XP may struggle.
Whats slow, start up, general use or a specific piece of software.
If you have all the useless aero functions turned on then that will slow things down, drain the battery, maybe its bogged down with adware, maybe you have lots of software all with auto updates turned on all vying for your internet connection .
When I used vista the only thing that was really slow was large file tranfer speeds, but I believe that was sorted out some time ago, 7 has its own set of unique problems but its operating speed doesnt seem any different to any other previous release of windows and I have used them all.
Speed is nearly always down to a combination of hardware spec and setup.
Vista will only be "erased" if you tell the new setup to erase/overwite it with whatever Op/sys you install