Did you save the .png as an .ico file with Irfanview? I'm not sure how that program saves .ico files but when I tried they didn't work right. I suggest you try a dedicated icon program to convert your .png files. I like IcoFX:
http://icofx.ro/
As for using the icon in UltimateLaunch, did you initially set up the icon as a Program Icon? If so you have to delete the icon/program from the tab and add it again as a XP-Icon. Hopefully that will fix your problem. Also, if you need any icons check out my signature.