I usually do design stuff and i sometimes run dreamweaver, photoshop, indesign or flash.
WOw, there's your problem. Those are all Rosetta apps, which means they gobble up even more memory than normal. You really should get 2GB, but if you can't afford it right now then buy one stick of that 1GB G.Skill RAM I linked to above, which will give you 1.25GB. Then, later, buy another stick and replace your other 256MB one and you'll be up to 2GB.
Just for your reference, here's what's running on my 2GB iMac right now:
- 3 FireFox windows with a total of 19 tabs open
- MacroMedia Fireworks 8 (Rosetta)
- TextMate with 10 files open
- Terminal
- Locomotive
- Safari with 3 tabs open
- Adium
- iTunes
- Parallels (384MB dedicated)
- Skype
- VirtueDesktops
- Growl
- Quicksilver
- MenuMeters
- 4 dashboard widgets
- Steermouse
That's using about 75% of my 2GB of RAM. Out of all those apps, Fireworks is by far taking up the most memory -- almost 400MB with several files open. I can't even imagine what your system must be like when you have even TWO Rosetta apps open, let alone all four. When I started out with this machine it had only 1GB, and when I got going on on development stuff -- especially when I had a Rosetta app like Fireworks open -- it was bad. So get the most memory you can. At least buy one 1GB stick now, if not two.