Seeing as this post has gone unanswered for a while now, I'll give it my best shot.....
Your P2 may or may not run it. It really depends on the size of the drawings that you'll be working on. By size, I'm actually referring to more than just "8x10" or "20x30". I'm referring to the ppi (Pixels Per Inch). This is often overlooked. It's very important, specially when you have a canvas (in the program) that is large. A blank canvas that is 11 inches tall by 17 inches wide and is 400 ppi would be 85.6 megabytes in size. That's a large image (file) for an older P2 to handle. Now, lets say that you will be (or are) using Photoshop CS. When you apply a filter, it will have to render the entire image. This will be painstakingly long, and might lock up the computer. These sizes that I have given aren't really far fetched either. An image printed at 400 ppi (dpi when printing) is standard for a top quality printer (Fuji Pictrograph 4000-II), and 11 inches by 17 inches is a standard large size for a picture that doesn't require any special frames.
If you don't plan on making anything to print, and only for web use, then you can work at 72 or even 100 ppi, and I think that you'll be fine.
If you do plan on making larger images for printing, then I'd upgrade to a new machine that is extremely RAM happy (2 gb min would be ideal, although you'll find that 1 gig will be fine), a 2.8 P4 with 800 mhz fsb (or equivalent AMD), and a large hard drive (or dual drives would be better, specially if you use Photoshop as it likes it's own scratch disk seperate from Windows), and a midlevel graphics card (64mb minimum, as since art is 2 dimensional, it won't require mass usage, if any, from a graphics card, but a graphics card will help to free up resources for the computer to put towards the editing program).
Card/letter creation can be done right from Photoshop and most other photo editing programs. There's also some programs made just for creating cards, which should work fine on your P2.
I don't know to much about CAD programs (achitecture), but I've been told that they're rather demanding on a computers processor. If this is the case, then I'm afraid that you're P2 probably won't do well.
If you're going to draw on the computer, then I'd also recommend a drawing tablet, perhaps from Wacom. Also, if you're going to be spending hours in front of a computer screen, then I'd recommend a CRT (like most tv's) for a monitor. Reason being is that you can adjust the Hz to 85Hz on most monitors, which will help to avoid headaches, and reduce lines on your monitor/image due to flourescent lighting.
I hope this is what you were looking for in a response and that it helps you!!!