You pretty much have to judge what you do by how much RAM you need. Have copies of Bryce 3D, Photoshop, Illustrator, Lightwave, Maya, 3D Studio, or other intensive 3D graphics applications on your hard drive? If you have 2 or 3 of these then yeah having an extra 256 would be a great benefit to you. I have 256 megs of ram on the setup you see below but running 4-5 copies of IE, netscape. winamp, icq, aim, and few other things in my systray, no matter how much I have going on I ALWAYS have complete control of my system with no slowdown. I'd do some tweaking on your current system before you go and spend another $180 (I hope you spend at least this much to get QUALITY ram) on 256 megs of ram.
Make sure your ram is running at cas2-2-2. If it is, and you want to overclock, tweak your fsb to run as high as possible at these settings. What hard drive are you currently using? The two fastest drives on the market are the IBM Deskstar GXP series of drives and the Quantum Fireball Plus LM series, respectively. If you don't have 7200 rpm and at least ata/66 drives (the IBM's are ata/100) then make this upgrade first, I guarantee if you're running slower drives you will notice a difference in load times on your programs. I have the quantum drive myself and absolutely LOVE it. Benchmark runs at about 17000, where as the average ata/66 drive benchmarks around 13,100 so I am extremely happy with the performance of my drive.
Also try messing around with your swap file, since you already have 256 megs of ram, if you are using a flavor of win9x/me then set this in the [386Enh] section of C:\Windows\System.ini
ConservativeSwapfileUsage=1
Then you will also want to set a permanent swap file size to 256mb of ram (increase this to how ever much ram you have) in case Windows does somehow manage to use your swap file. Generally this is unlikely, however, possible if you have crazy uptimes.
divinemartyr