10.4.9 install and new iTunes+iChat made iMac unstable

Question

Guys, I need your knowledge.
I bought my computer March 2006, and since 2 weeks ago, it was perfect. I don't use it much, except for the internet, writing stuff, listening to music, and playing a few games (HoMMV!). I have not installed Windows XP on it...to me, that would defeat the purpose of having a Mac.
In any case, two weeks ago I downloaded 10.4.9, plus the newest versions of iTunes and iChat. Since then, I hate my Mac! It's running very erratically. After being on for a few hours, if I want to start iTunes or iChat, the applications take a few minutes to start-up correctly, whereas it usually took 3 sec before that. Sometimes, these applications just won't work, so I have to constantly restart my computer, to "reboot" its power. Inserting a CD or DVD is also half-hazard. Sometimes it takes several minutes for the computer to read the disc. VERY annoying!
And even when I do restart the computer or shut it down, I almost ALWAYS get a gray screen asking me to hold down the power button. I feel like I'm on a crappy, erratic Windows machine nowadays, and I hate it! I wish I could turn back time, and not have downloaded the updates two weeks ago.
What can I do to fix the problems? I knew nothing or repair permissions, archive & install, etc, before reading these forums. I thought I didn't need to go through all that crap with a Mac just to browse the web and listen to some music. Is there any hope that my Mac will regain its former superpowers, or am I doomed with a sub-par and unreliable machine forever on? Are there patches coming up to fix these issues?
Thank you in advance, for any kind of help.

Answer 1

Hey again,
I tried your suggestion of installing the combo upgrade (wasn't that what I had already done?) and repairing permissions afterwards, but my computer still doesn't work too well. Again, after being on for an hour or two, if I need to open iTunes or iChat for the first time, it still takes forever. And from time to time, I still get a gray screen in many languages asking me to hold my power button when I restart or shut down.
Will reverting back to 10.4.8 solve my issues, which I never had before? Could I always revert to ulterior versions of iTunes and iChat? And I appreciate that page about kernel problems, but there's so much to read! I always thought Macs were for people dumb with computers; which is why I got into it 5 years ago. Basically, I want these nagging issues to go away, but with a minimum amount of effort and hassle. For example, I don't backup anything, I don't want to buy an external hard drive in case things go wrong. I could copy my schoolwork and music on DVD if a new installation is required, I guess.
Any more inputs, pretty please?!