Are you getting errors Mike? If so, what are they?
I actually worked with Microsoft on one of the issues relating to Vista SP1 early on, regarding problems installing it on a dual boot set up.
You must first make certain that you have installed all other windows updates before attempting to install the service pack. The reason for this is that the update site will also present to you any device driver updates during the scan.
Upon first release of the service pack, microsoft listed 12 specific drivers that could cause problems for users during an upgrade to the service pack. Most of those however have already been addressed but if you have not installed all the updates that are made available to you then you could be the source of your own issue.
Two other issues that arose, while I was working with microsoft regarding this very problem that you are experiencing, is that I discovered at least three (at that time) antivirus applications that prevent a successful install unrelated to the hardware driver issues previously mentioned. These were Norton, Mcafee and Antivir.
For those, the recommendation was to have uninstalled the applications prior to installing the service pack due to the nature of microsoft's poorly written code for the upgrade's unattended reboot pattern.
Disabling these is not recommended either since they will reclaim their active guard upon the first reboot which will stall the installation and create a reboot loop from which there is no escape. Some users, depending on what other applications they have installed, might find safe mode will stop the reboot loop but this is not always the case. For those unfortunate few, the only alternative at that point is a fresh reinstall of the operating system.
The other issue relates to the order in which you should install the windows updates that ARE presented during a scan. The particular order should already have been selected for you. You should notice after a windows update scan that certain of the boxes next to the available updates are already checked. There are three of these that you should uncheck (more on that in a bit)...and you should NOT check any of the boxes that are not already checked.
After the scan, click to review the available updates. Look for the service pack 1, the malicious software removal tool and the .net framework and uncheck them. Install ALL of the updates with boxes checked by default except for those three...save them for last.
Reboot if prompted. Return to the update site and scan again. After the scan click to review the available updates and once again, look for the three items, sp1, msrt and .net framework and uncheck them.
Again install all the others that were checked by default except for those three. Reboot if prompted and return to the update site...continue in this manner until you have installed all of the updates except for those three mentioned.
Of those remaining three updates, you should install them in this order:
1) .net framework
2) malicious software removal tool
...and, on a side note, as you can see from the info above, it would be pointless to try and create a slipstream disk unless of course, you merely wanted to create a folder to hold the SP1 installer file.