this board has lots of info on credit, including cards, inquiries, etc, so go there to do indepth search:
http://www.creditboards.com/phpBB2/viewforum.php?f=2

in regards to your actual questions, each time you apply for a card, a 'hard' inquiry is generated on one or more of the three credit bureau files that are maintained for you. More than 2 inqs in a 6 month or so period will start decreasing your 'fico' score, usually by 2-3 points per inq. While this may not seem like much, if you're on a threshhold of one level of scoring going to a lower level, anything that pushes you over the edge should be avoided.

Hard inqs stay on your credit file reports for two yrs, but only affect your fico score for 12 months.

To get your TRUE fico score, you should go here and only here to do so, as other 'scoring' sites generate simulations that are often nowhere near accurate.

goto www.myfico.com
skip all the Suze Orman crap and select ONE report to buy:
http://www.myfico.com/Products/FICOO...n.aspx?fire=24

here's a couple discount code to try, for 20% off:
'myfico132', 'myfico20'

I've never ordered the 3 at once, i always order each up separately(don't remember why, but there used to be some reason for that); anyway, each credit file is likely to be different, therefore generating different fico scores.

You wanna go to myfico.com to get this, as this is the only site that accesses the credit files and applies the true fico scoring algorithm to your file. All other sites are fake...

There is a WHOLE lot more to this than i've outlined, but this should get you going...