Check your /boot/grub/menu.lst and make sure it says splash=silent not splash=verbose.
example:
kernel (hd0,4)/boot/vmlinuz-2.6.32.10-pclos2.bfs BOOT_IMAGE=2.6.32.10-pclos2.bfs root=UUID=ba2a471a-6050-47d3-8394-51cb0d065f3f splash=silent vga=788
If that looks ok then maybe open a terminal konsole, su to root and type switch-themes PCLinuxOS
If that doesn't work then you must have some kind of video card that plymouth bootsplash cannot use.