I'm new to Adwords. I just composed an ad, and specified in Google that I want to target the ad for a choosen website. I put the minium with is $.25 per thousand impressions.

After waiting four hours, when I went into the reports, it shows that I got zero impressions and zero clicks.

Why is Google not displaying my ad? Do I have to wait a day or two for the ads to kick in or do I need to increase my the amount that I am willing to spend per thousand impression?

You might need to wait 24 hours for the report data to show - I don't think those are live up to the minute.

May be 0.25 per thousand impression should not be sufficient for displaying ads

shabbirbhimani is correct. You're bidding against anyone who wants to pay more per relative keyword. Quality Score and CPM are the biggest factors, in that order, which determine if your ad will show verses the competition's.

for your ads to show on the content network they must be screened by adwords. it can take anything between 1 sec to 24 hours. after that you would have to wait for about 3 hours approximately depending on your timezone to start seeing data...

ya... the bid may be low... but i guess that depends on the site... how long is your list of sites?

I was just targeting one site. Turns out that nothing is wrong. My bid is too low, so other higher-bidding advertisers took all the slots on that site.