internet question



Could somebody pls help me with this issue...?

I have a 12 inch PowerBook (G4) and I am running Os X 10.1.2
I am connected to the Internet via light-speed cable connection, using Internet Explorer. My firewall is turned on.
The problem is that I get this security notice more often than not, that says:
"Unable to establish a secure connection to site. There is a problem with the security certificate from that site. (The identity certificate is not yet valid.)
The information you view and send will be readable to others while in transit and it may not go to the intended party." After I click on the Continue botton,
a message appears that "The server cannot be found".
My ISP provider is clueless as to how to fix the problem. I tried to remedy the situation by downloading Safari, but turns out that I would need a more recent version of OS X...Any solutions for that without having to buy software upgrade?
So, I guess this turned into two questions.

Thanks in advance!
Trash Internet Explorer and empty trash. Use Safari, or if you must be counter-culture, Firefox.
Thank you so much! About Safari; I am under the impression that this is a free program downloadable from certain Apple sites. Is that correct?
Why are you still using 10.1.2? Use software update to download the "free" 10.1.5 update. That will remedy some of your problems.

Overall 10.1 is a terrible version of OS X to be using on your PB. It's so outdated. Just go out and buy 10.4. That will cure most of your problems as you will have current versions of your software.

If you want a current version of Safari you have no choice but to buy Tiger. The only version that is available for download is 1.2 at the link below.
I appreciate your help!

Looking at your reply, I guess my user name should have been "Dinosaur" instead, ha-ha! But if you care to know here is the explanation:

When I bought my PB I was switching over from PCs. I also bought Adobe Illustrator along with it. Everything was working perfectly, but because I use a lot of PC-based programs (AutoCAD, etc.) I was still using PCs for Internet and such. Now I am trying to make "the total switch" and started to encounter all these problems. Also, at work I am the only one with a Mac, so there isn`t a lot of help available around me.

So, I am going to get 10.4. Thanks again!
Didn't Safari require Jaguar or higher? 10.1.x is like 3 years old, you should give Tiger a shot :p