My view has always been that any windows updates should be done prior to installing any Service Pack.
Follow these instructions -
To resolve system file issues, use the System File Checker tool (SFC.exe) to determine which file is causing the issue, and then replace the file. To do this, follow these steps:
1. Open an elevated command prompt. To do this, click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.
2. Type the following command, and then press ENTER:sfc /scannowThe sfc /scannow command scans all protected system files and replaces incorrect versions with correct Microsoft versions.
Following the operation of the “System File Checker”, I would revisit the Microsoft Update site again to scan for and download any updates, then would try (again) installing Vista Service Pack 2.