My 2000 528i has trouble turning over atleast about once a day..it eventually cranks on the first try but takes awhille. Wats wrong?

Take the car into auto-zone and have them preform a check on the battery . It is called a load test . It will tell you the state of the battery and it if free. If the battery is over 3 years old it might be time for a new one. And thy will test the other charging components at the same time

Your starter may not be the problem if it doens not even click when you first try and it does not crank. You many have a bad SLOW ignition switch its more common than you think.

Do you mean it turn over slow and barely starts or turns over as normal but take some time to fire?

If it turns over slowly take the advice above and get the battery tested. I don't know about Autozone though... I try a place that specializes in batteries. Here I use a place called the Battery Exchange. Check your Yellow Pages.
If the battery is tired be sure to replace it with a Johnson Controls product like Interstate and not an Exide product. Google Johnson Controls to see their range of battery products. The battery in a BMW is not a place to get cheap.

If it turns over as normal but doesn't fire immediately then it is probably the check valve in the fuel pump. You have two options. Replace the fuel pump ($300) or install BMW's retrofit designed for the 750iL ($15).
It is an external check valve that installs over the fuel pump and takes all of 30 minutes.
Part number 16149068988 right from BMW.