Many things could be affecting your ability to quickly download and open an
Excel workbook over the internet.  The speed of the server (where you are
getting the file from) controls some of it, the quality of the connection
from there to your computer has some effect on it.  The amount of memory in
your computer can also play a role in this.  Windows XP is very good at
optimizing an internet connection, so 'tweaking' your system is probably not
needed.

One way to check to see if your connection is all that it should be would be
to run some on-line speed tests from reputable/reliable speed test servers.  
This page has several available though it:
http://www.dslreports.com/stest
If you get 70% or more of your 'rated' speed, you have a good connection.  
Lets say RR says you have a 4Mb/512Kb connection, then if the tests show you
are getting anything above 2800/358 then things are ok.  Even if the test
shows lower than that, time of day can also play in to it: run several tests
from the same location(s) for a couple of days at different times before
passing judgment.

If you have any questions about that or think you have a problem with your
RoadRunner connection, the folks at this discussion forum can try to help you
figure it out: http://www.dslreports.com/forum/cable,rr you don't even have
to create an account to ask questions and get help there.

I don't think, at this point, that this is an Excel problem - not unless
loading .xls files that are on your computer is also taking a very long time.
Is this a new computer?

Tough one.  For now I would treat the two issues as separate ones.  The
internet speed issue is probably not related to slow loading on the computer.

Many new computers come loaded with a lot of sample and demo software that
you don't even need (and may not even want) running.  Determining what is
running on your computer is going to be difficult to determine here in this
forum.  You may have something running on the computer that is slowing things
way down and it will be difficult to determine here what should be running
and what doesn't need to be that could be a slow down.

Can you describe the computer in terms of its brand/CPU/memory size?  You
can find out about the CPU and memory by right-clicking on My Computer and
choosing [Properties].  The first [General] tab that shows up will have the
CPU and memory information in the lower right portion under "Computer".  Like
this home made machine I'm on right now says:
AMD Athlon(tm) 64 X2 Dual
Core Processor 4800+
2.41GHz, 2.00 GB of RAM
Physical Address Extension

Did Office and Excel come installed on the computer or did you put either of
those on it after your purchased it?

Do you have any other Excel files on the machine, and if you do, do they all
load slowly or do most load swiftly and just that one loads slowly?