Building a new pc, need advice.

I hope i have posted in the right section.

Not my first build, fairly savvy, but not compared to people around here, so thats why i come hat in hand for advice, lol.

I have a P4 2.4 northwood, socket 478, 1 gig ddr, MSI MS-6728 NEO2 mobo with intel 865 chipset . I havent really kept up on whats going on in the tech world, another reason for this thread.
I do the standard stuff, internet, email, downloading, uploading, bit of video editing. I dont do intense games so i will likely use either built in video or a cheap agp or pci vid card that i already have.

MSI was good to me, replaced my mobo for free after the warranty period, so i would try and stick with them if possible for the mobo. And, as far as i can see, my MSI mobo has been great. I think one can get a decent MSI mobo for a fairly low price? Thats my impression but if im wrong please tell me!

I am thinking what i have to buy is new ram, new mobo, and new cpu, and maybe a new sata hard drive. Also perhaps a new power supply. That would depend on the situation as i do have a couple decent enermax ps's around, but only 20 pin. I believe i can convert it to 24 pin?

I have pc cases, ide hard drives, video cards, usb2 and firewire external boxes for hard drives. If there's a reallly big advantage going with sata over ide then i will need at least one sata hard drive.
Or should i wait for sata2?

Where is the best bang for the buck in the cpu arena, intel or amd? Since i have a 2.4 mhz cpu and thinking of the rule of thumb that one should really double up the cpu speed when building or buying a new pc, where does that leave me?

I have tended to go with a small, say, 80 gig hard drive for my os, then another similar or larger size hard drive for my data, then a compliment of usb and firewire drives for backup, archives, music,and data. Is this still a good way to go?

Any reasonable info/advice will surely help as i I need to learn which way to go here on this new build and i know some of you here will come up with info that will save me money and help me get the best speed and reliability. Money is an issue but there is usually that sweet spot where you get the most for the least, so i suppose that is where i should be in the dollar department.

Oh, and i will be using win vista ultimate os, which i already have. And i have a Samsung 19 in widescreen lcd monitor, decent mice and keyboards on hand, so i dont need any advice on those items.
I also already have a compliment of dual layer dvd burners, cd burners, dvd rom.
I guess i should point out that i am in Canada, but i can order on the net from most U.S. onlines anyway. These days its a real advantage!

Thanks in advance for your help/info/advice/opinions.