What this is saying is that the disk where the spooler file is located doesn't have enough space to spool the file. This disk could be either the Win 98 computer if the HP is directly connected, or either the Win 98 machine and/or the print server if the HP is connected to a network.
The default location for spooled print jobs in Win 98 is \Windows\Spool\Printers and \WINNT\System32\Spool\Printers in NT4 and Win2K.
If the disk on which these locations exist is getting tight on space, you may need to either move other files elsewhere to create sufficient space or move the print spooler location to another disk.
Also be aware that a printer (especially color printers in my experience) may actually create a spooler file many timesthe size of the original file.