His motherboard would have 1.1. All Core 2 chipsets had that. In this case it's more a problem of BIOS compatibility. Not knowing the exact motherboard it's hard to tell, but yes, there's a chance that a modern GPU will have problems with an old MB.

No problem :D You can necro this as many times as you want. ;)

This is also interesting subject - I didn't know that 2.0 could have troubles with lower versions (and the new card, as it says on its box, is 2.0x8). Anyway, I have already this card and I can't see any problems so far - I've already played third person view game for a pretty long time, with nice amount of fps. My mb is Asus P5K-E ("according to the internet" 1.1x16).

Might be worth checking to see if there is a BIOS update then. If it's a 1.1 port, then it should at least work with a 2.0 card, though make sure to check first to be on the safe side.

Glad to hear it's working. If it's working and you played a game you shouldn't worry about compatibility problems. These normally show up very early.

Ah, I was going to ask: how long I should wait for there problems to arise.
But if you are saying "very early" then indeed they should be visible already I think as I played a few "pretty long" sessions. :)

btw: What kind of problems could be these? PC stops working? Artifacts on screen? Blue screens?

Typically it's up front "PC doesn't want to boot" kind of thing. For PCIe 1.0 it might be different, because it provided less power to the card, so possibly it would fail when running games but not for the desktop.

Anyway, googling found this post which says that NVIDIA is actively trying to maintain compatibility with 1.1, and AMD doesn't. (At least at the point the article was written, about 2 years ago.)

In case of a 1.0a port with a later card, you'll simply not get a picture.
If the card is not getting enough power it will probably make demanding games stutter. This was at least what happened when I forgot to plug in the power cord from the PSU to the card a long long time ago.

Ah, so if it's already working it should work from now on :)
This article is a very good find! One thing I noticed: So it seems that only cards with PCIe2.1+ could cause any trouble? On my card's box it says: PCIe2.0 - it's another thing which causes me to think "it will be ok".

(but still, in one of above posts there is this link and it has 3.0 mentioned in it... sigh... still, I hope 2.0 is closer to the truth)
As we can see here card with GDDR5 have another advantage over card with DDR3 - less power consumption/requirement. So it was also good I bought GDDR5 card as it should help my system overall / less chance to fail.