I think you will find that using any other connection manager than DLinks buggy connection manager will solve most of your problems. As a matter of fact, the latest drivers from DLink no longer use this problematic program. Just use Windows connection manager and see if that won't help.
Furthermore, an updated driver from the support site for techs, and not available to uninformed customers »tsd.dlink.com.tw/ may be of help. DWA-552 driver here http://tsd.dlink.com.tw/downloadsmodel.asp
I noticed that there was only one driver on the regular customer support site in 2008 (v.1.30) but several old ones in 2007. This is unacceptable... customers should have access to the latest. On the site link referenced above, you can find v.1.40. When I installed it, all of a sudden I got a "very good" connection (4 bars!). Previously, all I got was 2, and along with that some Windows issues.
edit: I moved this card to another machine since this post, and it won't assign an IP. Good signal strength, just won't latch onto an IP. This is with the latest driver that updated the previous buggy connection manager. So I go from one issue to another.... it's like playin' "Whack-a-Mole"!!
This 552 card has some serious problems.