If you find you need to include quotes on the command line, there are several ways to go.
1. Use single quotes outside and double quotes inside.
SHELL '%comspec% /c "C:\Program Files\Internet Explorer\iexplore.exe" about:blank'
2. Use Chr(34) in place of double quotes.
3. Assemble the shell command as a string.
$ShellCMD = Chr(34) + $WorkDir + "\symcdefsx86.exe" + Chr(34) + " /q /extract /vdb " + $TempDir
Shell '$ShellCMD'
The difference between SHELL and RUN is that RUN returns to the script immediately and allows it to continue. SHELL normally will hold the script untill the shelled program terminates. In some cases, the shelled program calls another and terminates, returning control to the script prematurely. Using Start /W could mitigate that.
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