You can effectively do it with SBB.
Step 1 : Use Flicster to export the storyboard
Step 2 : Launch SBB, click on the munit button in the first window
Step 3 : In the munit window, click on the radio button corresponding to the "Alone" formation.
Step 4 : Click on the "..." button in the first line (in the group with 6 lines), select the PCX file corresponding to your storyboard
Step 5 : Change the number of frames if needed
Step 6 : In the preview area, change the zoom factor (default is 100%, you can increase of reduce it). The preview will show the result, so it's easy to adjust.
Step 7: Change the output file if you want
Step 8: Export the pcx.
Step 9: In PSP 6, open the pcx (it's a true color pcx), and change the palette to what you need (normally the one from the export by Flicster)
Step 10 : go back in flicster to produce the FLC (don't forget the size has changed, so you cannot use the initial fxm but you need to make a new one)