if you are going to reinstall a clean windows i recommend this ;
first install windows and your key programs
using a copy of partition magic or similar make a second partition on your
hard drive. (partition magic does this without losing the data you have
already installed).
then when the machine is getting slowed down and cluttered up with junk
programs then copy the second partition over the first one.
This makes no sense at all, for several reasons.
If you want two partitions, don't start by making one partition that
fills up the drive and then change it afterward. Partition Magic isn't
at all required to have two partitions. Simply create a partition
smaller than the drive's size when you install Windows, then create a
second partition in the unallocated space afterward.
Second, the concept that the machine will get "slowed down and
cluttered up with junk programs" is completely false. Although it
sometimes happens, it's far from inevitable. With a modicum of care,
it never happens, and Windows doesn't need to be reinstalled or copied
over from another partition
Third, what you are essentially suggesting is a backup of your Windows
installation in a second partition. This is a completely
unsatisfactory backup scheme, as far as I'm concerned. It's better
than no backup at all, but just barely. I don't recommend backup to a
second non-removable hard drive or a second partition because it
leaves you susceptible to simultaneous loss of the original and backup
to many of the most common dangers: severe power glitches, nearby
lightning strikes, virus attacks, even theft of the computer.
In my view, secure backup needs to be on removable media, and not kept
in the computer. For really secure backup (needed, for example, if the
life of your business depends on your data) you should have multiple
generations of backup, and at least one of those generations should be
stored off-site.
Fourth, in the instructions you provided, you neglected to explain
that copying the second partition over the first one will cause the
loss of all data files, all applications installed since that initial
backup, all customizations to Windows and application programs that
have been made, etc.
And finally, you've made such a recommendation without knowing how
large a hard drive the OP has. Not everyone has a drive big enough to
waste half of it for what you recommend.