Overclocking. Have I damaged my system? Help is appreciated..

The other day I overclocked my videocard (Asus Geforce Ti4200)
and in the middle of the process I realized I hadn't done enough research before I started to fiddle around with it, and that I didn't have a clue what I was doing. That's exactly what all guides on the subject warns you not to do, because it can damage your system.
My question is: If you overclock a card incorrectly, does the damage occur instantly, or does the new setting have to be applied for quite som time before the temperature rises to a damaging level? And: If the damage has already happened, is there an easy way to find out, or do I just have to guess if a system crash is due to a damage to the videocard or just a software-failure? Will a hardware damage always show up in "Device manager" or are there cases where the video card could be damaged, and it still wouldn't show up in device manager?
I just left the overclock on for maybe 10mins or so, but still I'm worried that I have damaged my system in some way. My Windows XP installation takes extremely long time to close down, but I don't know if this is due to a hardware failure or just a badly programmed program I've installed (what kind of errors can one expect?). I would appreciate all help on the subject.... Thank you.

-Hal

Yes, you should not O/C until you understand the process.

Truth is O/C'ing a vid card is pretty simple. First off ensure you have adequete cooling..does your case have good airflow(intake/Exhaust)? What are your case temps and cpu temps..this will help you know how warm your case is and if more fans are needed. Generally our rigs here are 45c(average) load(air cooling) and mobo low 30's or 20's. So if your mobo is 30c+ and cpu in the 50c+ range that means your case is pretty warm and o/c'ing your vid card is not a good idea.
If your case is cool and has good airflow does this airflow include the AGP/PCI slots?
Generally this part of the case can be a dead spot for air flow and heat can be a problem especialy for newer vid cards. Most new cases have a fan on the side panel to cool the pci slots.

Once you determine that your case has good airflow and your vid card is reletively cool than time to O/C
We generally increase the clock/core small increments at a time and then test a game or 3dmark2003 to see if the O/C was stable. By stable we mean are there any artifacts or tearing. When you use a 3d application does the screen have white spots? Lines across the screen or anything else that was not there before you o/c'ed? If so roll the clock back a little, if not increase a little bit more. To save you the trouble most of us w/ a Ti4200 get 300/600 on average. It is okay to jump to this number and test from there. If you do get lock ups...press ctrl upon the boot up process..this will reset your vid card back to default clock speeds.
Your ASUS card has good stock cooling so no worries there. Some of us add ram sinks that you can make yourself out of a old HS or buy a VGA cooling kit that includes them. I doubt you want to go that extreme right now. But the ram sinks do help to transfer some heat from the ram modules and this means you may be able to push your O/C a bit further


My ti4200 is at 300/600 and i keep it this way! I have ram sinks and 80mm samrt fan keeping my pci slots cool...I have very few artifacts(only BF1942 has occasional tearing) and no slow downs nor lockups!
HAPPY OVERCLOCKING DUDE!!!!