If you can, wait a couple weeks for Intel Core 2 Duo (Conroe) CPU systems to hit the market.
Look for price drops on other systems, too (Intel Pentium D 9xx, AMD Athlon 64 X2).
Celeron and Sempron CPU's? Stay away from those for your needs.
You can always add more RAM to one of those new systems.
BTW, what is your current video card?
I'm currently using a Sony Vaio Pentium 4 system and I'm finding that Photoshop & Illustrator CS2, Serif PagePlus 11 and MS Publisher 2003 are running rather slow. (You wouldn't believe how slow a page re-format gets with MS Publisher 2003 on a 300 page document!)
The system could only handle 1GB of RAM and I'm seriously considering upgrading in the next few weeks. I want a system that can handle 4GB of RAM but I'll settle for 2GB to start, but I've never really understood the difference between the Celeron, Pentium and AMD CPUs. Obviously, I'd like the best buy I can get, so I'm leaning towards a Pentium D system with a 300GB SATA drive and either a 19" or 20"(widescreen) LCD monitor, but could I save a few bucks and get the same performance using a Celeron D system?
I use this system for writing (novels), editing (digital photos up to 12 megapixels), creating (Photoshop and Illustrator images) and some programming (Borland Delphi) as well as cruising my favorite Photoshop and fiction forums.
Could someone give me a breakdown of what the differences are and why I should spend more? I've seen the local Fry's Electronics offering an HP a1530n Pentium D for $729 - sans monitor and only 1GB of RAM.