I made new hack on b2upload.php file because any hacks from this forum not working mutch well. Hack is based on old B2 upload hack and has lot of improvements.
+ No imagemagic (GD only)
+ Truecolor thumbnail image creation
+ Ratio image (thumbnail) resize. Images wider or higher than $MAX_SIZE will be resized
+ Script use low quality functions if high quality functions not supported
+ Small additions in stat part and litle thumbnail is shown on upload form page
+ openwin.js file added (JS to open new window thumb.php)
+ File thumb.php added. File show fullsize images as JS popup window.
Window automatically resize to image size
Download WordPress b2upload.php hack