To the OP,
Who asks---what will prevent--adjust the volume/soundcard settings, display settings, disable the antivirus/firewall and install applications. Thanks.
I know that a limited account in XP pro will prevent the latter two---but I am guessing even a limited account would not prevent messing with volume settings.
Having my computer in my own home basically prevents me from needing a limited account to prevent unauthorized users from using my computer---but anyone who has a computer
in a public space should prevent unauthorized use by password protection on all accounts at a minimum.
But what should not be missed here is that there also other compelling security reasons for even the main user to use a limited account most of the time. And that reason, in a nutshell is, that if some sort of malware gets by whatever security you have---it can do little or no damage on a limited account---but unlimited damage on a administrative account. And if you need administrative level privileges to do something---use fast user switching to log onto an administrative account---and then switch back to limited when you are done.