Yea, i'm working with php4. I tried switching to php5 (the app works the same on 4 and 5, but production environment will be 4, so i use that) and it did not work
And equally: I have the folder where sqlt09a.dll resides on my system path. I tried to reinstall xampp and informix this weekend just to find the same problem. Will keep trying whatever comes to mind and post my experiences.
Anyway, thanks for your help.