As long as you have the install CD-Rom you can delete it. You can then edit
"SourcePath"="D:\i386"
(where D is the drive letter for your CD-Rom)
found at
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup
Some things to check;
Clean out your %windir%\Temp, and \Documents and Settings\%username%\Local
Settings\Temp directory. Delete the Temporary Internet Files, and History.
Do you have a disk defragmenter, if not get one and use it. You could use
Find|Files/ Folders and search the drive for; say files greater than 5mB and
then decide if they're needed. Check the %windir% directory for a
$NtServicePackUninstall$ directory, if your current service pack is stable
and you don't anticipate backing down, you can delete the dir. Also check
for the existence of User.dmp and Memory.dmp (both, by default should be in
the %windir% directory) you can delete these unless your going to send them
to the application vendor, or Microsoft for troubleshooting purposes. Other
options are; moving the pagefile to one of the other drives, uninstall your
programs that are installed in C:\Program Files and reinstall them to
D:\Program Files If you have a lot of local user profiles stored, you can
move them, see this article for info on this.
How to Move the Location of a Locally Cached Profile
http://support.microsoft.com/support/kb/articles/Q214/4/70.ASP