Azure,
I note you are in Canada, so this info has to be read in context with the price & availability of parts there. I assume InFInRetirement did not notice this, as pommy prices are not much use to you.
1. The first question is as always *What is it to be used for?* If only for the internet, or wordprocessing, even a 486 is sufficient, however, if the latest games are the go, then the video subsystem is very dependent on that. The other big deal is whether you want to do heavy duty graphics work. That will impact the CPU and RAM requirements moreso.
2. Second major question is, *What do you want to outlay for this?*
Only when these two questions are answered, could anyone give appropriate direction on the hardware requirements.
You may want to consider building a new one for yourself, and the daughter gets the 450. You must know by now that as soon as you complete the thing, it will be obsolete!
Asking for future requirements ensures you get only one answer - get the best/latest/fastest that money can buy right now (i.e. Athlon/PIII 1000), but the cost?
Generally all things come down to a price/performance tradeoff. Only after you can answer question 1 & 2 could you get more appropriate advice. I ask this of all my customers who ask me that very question.
I await your requirements.
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When all else fails, read the manual!