Couple of points:

Vista with 1Gb is workable but runs a lot better with more, if you can
add in another 1Gb ( depends what the Medion WIM2100 can take ) then
go for it :-) Look at the amount of free RAM you have currently, 281Mb
is extremely low and the HD will be getting hit hard paging in and out
constantly !!

The Dell Dimension 2400 can only accept up to 1Gb physical RAM, i.e.
512Mb per slot. You have 768Mb so evidently the originally supplied
256Mb has been augmented with a 512Mb stick. The suggestion of going
for 4Gb RAM is just not possible on this system.

Having said that, the specifications *should* be fine with Ubuntu and
as you say 10.04 worked fine it's 10.10 that's having the problems.
Might be as well going back to 10.04 on it and perhaps giving 11.04 a
bash when the final release is out in April or just staying with the
long term support version ?

BTW - The 2Gb number on that Dimension 2400 is virtual memory and
that's totally different from physical memory.

I could stick a 2gb card in this laptop but I won't because I only
ever use it normally for teaching and demonstration and it putters along
OK for that. I am using it for Ubuntu just for email at present to my
Linux lists so again it suffices for that.

10.04 has not worked fine on that desktop with its 2gb RAM although on
this laptop it appears stable.

We do juggle titles for things.

In Windows the memory is displayed like that but to most ordinary users
know physical RAM as that memory stick you buy.

As it says the Physical memory is the RAM chips. Even if Linux calls
them something else. And the System read out in MS just lists the
computer use of that memory.

DRAM and SDRAM Memory Chips (210 companies)
Dynamic random access memory (DRAM) chips and synchronous dynamic random
access memory (SDRAM) chips are single-transistor memory cells that use
small capacitors to store each bit of memory in an addressable format
that consists of rows and columns. Because capacitors are unable to hold
a charge indefinitely, DRAM memory chips require a near-constant pulse
of current to retain stored information.

I do know all about this you know but i do hope it help other to have it
all thrown at me

but pretty much everything you have said on this topic
demonstrates that you do not, in fact, 'know all about this'. There is
a *vast* difference between the physical memory and the virtual memory -
not least of which is the fact that your CPU cannot directly access (and
therefore cannot have active processes running in) the virtual memory
and so the amount you have is irrelevant to any performance issues with
your machine - you could have several exabytes of virtual memory and it
would make no difference whatsoever. All that is important is that you
have 'some' virtual memory.

The *only* figure that is relevant is the physical RAM figure - you have
768MB of RAM in your machine as reported, correctly, by both Ubuntu and
Windows.

As an aside, even if you were right in your assertion that the virtual
RAM counts, you'd still be wrong as physical and virtual RAM are
reported separately and so you would, in fact, have 2.75GB RAM and not
the 2GB you keep claiming.

Having said all that, 768MB should be ample to run *any* modern OS
without problems.

I had 2x1gb chips but now have reduced it 2x512md chips. Lets see if it
freezes now And you can rest easy because I know what I am doing OK

your "Total Physical Memory" is what is installed.
Your first one says 1.00GB.
Your second one says 768MB

The second one is obviously using part of a GB for an onboard video card.
If you can add more memory you will see a significantly better system
performance.
The same could be said for both systems.

I have 2.5GB in my desktop and I still have freeze ups from time to time.
Mostly due to adobe flash.

You have to have a MB to take that extra memory, this one will not.

Generally speaking IF you can afford it max out the ram. Im running
2gb on my tower and this thing can outdo anything that I can bring up
against it.