Since I don't know how open your company is to purchasing a non-Windows system for you to use, I'll answer with two options. My qualifications are these: I've been using computers since 1983, pre-Windows days... and I currently keep my feet in both Mac and Windows platforms, am a graphics professional, currently self-employed.
Your system is completely inadequate for your needs. While Adobe will point out the MINIMUM required for running their software, if that is what you have, operations are sluggish at best, and "blue screen of death" at worst. They do also state what the "preferred configuration is", which is about twice that. I sympathize with the problem of trying to run multiple applications with what you have.
First suggestion, is, as one other suggested, get a Mac! However, you do NOT need the top end Mac to get the job done. Not even a dual processor. But the mini is simply not designed for a work environment and is a poor choice for your job. Macs WILL network beautifully with Windows systems, no problem there. I run a Mac/Windows XP system (wireless) with no problems.
HOWEVER, two other factors come into play here, when proposing a platform change to your boss: 1) Apple has just entered into an agreement with Intel for their next series of computers, so there will be "changes made". The good news about that is that Macs will stay on working for a LOT longer than a Windows computer, and you can go ahead and buy one of the current models without worrying that you will need a replacement in 12-18 months. 2) If you already have the Adobe Creative Suite for the Windows platform, and you switch to a Mac, you will be forced to buy the whole thing again, because Adobe won't let you "trade in or trade up". That's the BAD news.
Second suggestion: If you must stay with Windows, but on a budget... I'd want to know what sort of monitor you are currently using, and if you have and use a Wacom or other graphics tablet? Are you happy with the monitor you have? Get the best monitor you can, as large as you can. In a work environment where space isn't as much of an issue as it is in a small home office, I'd go for a high quality 23" CRT over an LCD monitor. An LCD monitor is good, if you can afford to get the best quality out there... otherwise, stay with a quality CRT.
I'd go for a system with the AMD Athlon 64 processor, and make sure I had 1 GB Ram, minimum, more if they'll allow it, like 2 GB. Windows is a ram hog, and Adobe programs always have been. Throw in MS Office, and your ram is gone... The Athlon 64's are speedy buggers, and if you pop in a good video card (you don't need a gamer's card, but a Video Card with own ram is worth it's weight in gold!), have sufficient RAM on the motherboard, and two HD's, you should be set. The reason for AMD Athlon 64 processor, over a Pentium 4 (don't even THINK of Centrino for graphics, you poor thing!), is that the AMD's are set for the next iteration of MS's OS to appear, whenever that is. It's already got the 64 bit architecture. P4's run hot, and the fans can be noisy.
Sony has come up with a new, cool way to keep the P4's cool, and they've put them into new systems called their Vaio Digital Studios. These systems also come with the Pentium D Processors, which are the newer ones. I've been looking at one. They run very quietly, have already got a video card in them, usually 1 GB already installed, a 250 GB HD, Double Layer DVD burners, USB 2.0 and Firewire, and both VGA and DVI ports on the back for your monitor. If you want an LCD monitor, then go for DVI, not the old VGA analog... you'll have better quality.
Do you have a lot of plug-ins for Photoshop, and fonts, loaded into your system? If you run Photoshop a LOT, and have a big plug-ins folder loaded up, it will cause significant slowdows too. Best to keep your plug-ins in another folder (NOT inside Photoshop's subfolders), and then tell PS where to find them. I keep my plugins and graphics, etc. on a completely separate external hard drive. If you don't have a Wacom tablet, I suggest you try one. I can't imagine working without one.
It's very late here, and I've probably forgotten a lot of things, but hope I've given you some things to think about, and for sure, make a list of "MUST HAVES" along with some "really wants", see how far you can go.
Best wishes to you... Firefly