Faith writes:
Problem is I don't have the tech knowledge or experience to do that myself.
Then a new machine (much like the second machine listed above) is your easiest, and best option.
Despite what has been said as to the ease of changing hard-drives, swapping floppy drives and replacing motherboards, if you have to ask what a 'Pentium' is then I would shrink from recommending you attempt these tasks yourself. At least the first time, unless you had a knowledgeable friend in the room walking you through it step by step.
While you CAN keep fiddling with a machine for years the useful life of a unit is around 3-5. After that then the technology has usually shifted enough to mean that a meaningful up-grade will, in effect, require you to replace enough of the core components that it is oft easier to simply buy a new machine.
For example a year or two ago the standard for connecting graphics cards (mini computers designed to solely handle the task of drawing stuff on the screen) to the motherboard changed from AGP to PCI-Express. You don’t need to know what these mean, only that to get the latest and quickest graphics card (PCI-E) you would need to get a new Motherboard. It’s odds on that the new motherboard would also have been designed to accept only the newer SATA hard drives, meaning you would have to buy new hard drives. As you have just replaced well over 60% of your machine you might as well go the whole-hog and benefit from a newer CUP and Memory (Ram). If you go that far then as the new CPU, motherboard and not least the graphics card will need batter cooling than your old case is likely to provide then a new case is probably in order; not least to house the new power-supply-unit (PSU) you will need to power it all.
Throw in the fact that having to swap out all these items yourself (it seems) would scare you witless then buying a new, better system is the best route.
Also as a new system bought from a shop, if it goes wrong then you have a service route and an avenue of complaint aside yourself. A luxury you don’t have if you perform the surgery yourself . .
A final comment I would say get the best system you can afford at the time as the better the system the longer it will remain useful before a serious up-grade is required.
Also make sure you get at least 1gig of memory. This alone will make your new machine a far nicer place to work..