Usually (but I don't know that HP) this isn't done in Device Manager, but with a function key or by running a program. After all, it should work also for the non-administrator user. What does the user manual say?
But another antenna (like that USB one) should work also. Be sure it comes with drivers for XP.
I posted some time ago that I am unable to Enable in Windows Device Manager WLAN, so I cannot pick up wireless internet. I am able to use my Smartphone to connect to my phone and get internet like that. If I purchase a USB that picks up wireless will this fix my problelm or not. I have now downloaded softwafe from HP and nothing corrects the wireless problem. I am running XP and mini has no warranty. I purchased it in this condition.