Very slow internet after installing 10.5.3

Question

Hello all, this is the very first time I have encountered any problems with my Macbook and I am hoping I can get some help here.
About a month ago I came home from college and hooked my Macbook up to the wireless router at home, everything was running fine. We have fiber optic internet so usually my speeds are blazing fast. Recently however I installed the 10.5.3 update and now my internet speeds are very dismal. I am having trouble getting my Macbook to connect to the router at all, much less load any web pages.
I have taken an ethernet cable and plugged my Macbook directly in to the router to see if things load any faster, and unfortunately things are still just as slow over a wired connection. After typing in a URL you will sit there at a blank web page for about 45 seconds to a minute before it even starts loading the page, and when the page does load it takes forever to pull up and images take even longer to display. If it helps at all our router is a dlink DI-524 wireless router.
I was browsing through these forums yesterday to see if I could find a solution to my issue. so far I have tried the following:
-set router to broadcast in G mode only (instead of mixed mode)
-removed encryption from router
-tried various encryption settings (64 bit WEP, 128 bit WEP, WPA, etc)
-updated the firmware of my router
-created test account on my macbook, opened internet browser on it, everything still runs slow
-deleted cache for safari/mozilla as well as the .plist files, still slow internet
when i called apple the agent suggested putting in my os X CD and do an archive and install, i did and once i was set back to os X 10.5 i was unable to connect to wifi at all, and wired connection over ethernet seemed just as slow as before. when i check for apple updates the 10.5.3 update was my only option, i couldnt choose 10.5.2 so installing that would put me back where i was before.
in the end i set my computer up last night to do a restore from my time machine backup. my machine has been restored to the backup i created just before i tried the archive and install, so im back to running OS X 10.5.3 now.
I'm sorry this post got so long, I just wanted to make sure that I included details of what I've done so far. Again I would like to stress that I am having this problem on my macbook even with my computer hooked directly to the router with my ethernet cable. (using that same cable and hooking up any one of my windows computers in the house results in fast and effortless web browsing so i know the cable is good)

Answer 1

It's not a matter of Mac OS X being "picky" but rather various ISPs not keeping up with changes in the DNS standard.
In the most recent case, 10.5.3 had to revert to a previous method of performing some DNS lookups because various ISPs hadn't bothered to update their servers to handle what has been the recommended way of handling lookups for the past eight years.
OpenDNS also has done a lot of work to make sure their DNS servers work as fast as possible; ISPs have absolutely no incentive whatsoever to provide fast DNS services.