I echo the other comments, sometimes the pixel definition won't allow you to do what you want.
However, there are different methods you can use to resize files, with varying results.
Most graphics packages resize using pixel resize algorithms. I don't have Photoshop 6, but you might be able to change the resize method to "bicubic" instead of "pixel resize". You should find this retains detail sharpness better, but even that has it's limits.
Also, in the older sims you sometimes found the settings in the panel.cfg put artificial limits on instrument clarity( the panel.cfg forces the sim to downsize even large, clear bitmaps). You might look at the panel.cfg & change the pixel size info to try to improve the definition.