if u r using Ubuntu 6.06 or 6.10, then dont worry. plug in the printer through USB ( i think 3550 uses USB). then turn it on. It might be auto-detected. if it is, gud enough. if it is not, then :-
System-Administration-Printing.
Settings:-
Local Printer
USB/LPT1
HP 3550 in the printers list
then install the printer.