Here are the specs:

-Hewlett-Packard
Pavilion
AMD Athlon XP 3000+
2.10 GHz, 448 MB RAM

Basically what I need to know: Can i upgrade my default monitor to a new/higher resolution monitor?

If so it is always necessary to upgrade my graphic card?

Is there a way to find out what resolution or display my computer cannot handle (example:LCD,FLATSCREEN,HD)

Any help is greatly appreciated my friend is quite lost on this one as am I

What is the model number of the Pavillion?

Basically what I need to know: Can i upgrade my default monitor to a new/higher resolution monitor?
yes

If so it is always necessary to upgrade my graphic card?
Not neccessarily, but you may not be able to get to a big LCD's native resolution(How they are supposed to run, look the best at) with an extremely old onboard.

Is there a way to find out what resolution or display my computer cannot handle (example:LCD,FLATSCREEN,HD)
It will plug into pretty much anything, The part you have to be concerned about is buying a monitor with the right connection. AVG, DVI or HDMI. I would imagine that most monitors still come with the standard blue(AVG) connection, but its been a while. If you buy the wrong kind of monitor (connection-wise) you can always pick up an adapter. Most new HDTVs have a PC connection(AVG) if you decide to go that route, cost effectiveness depends on how big you want your monitor to be, the picture is quite clear running that way.
like a 22" monitor is cheaper than a 22" TV, but a 32" TV is way cheaper than a 32" monitor.

Any help is greatly appreciated my friend is quite lost on this one as am I
Happy shopping

I'm not sure I'm attempting to rebuild my computer and help a friend at the same time i have tons of questions but this is the start.

My computer > General Tab > Says just this

Hewlett-Packard
Pavilion
AMD Athlon XP 3000+
2.10 GHz 448 RAM

He says the decal for his model name has been removed from the tower by a previous owner. I've been working with him through google looking for exact model just by appearance but have yet to get close. Seem towers with similar looks but more powerful performance wise. Thanks for all the help guys

http://www.gtopala.com/siw-download.html
Will show you a LOT about your system, Shows me my model number too so It probably will yours. And its free
The model number was under the system tab.

Problem resolved, Thanks alot : )