They don't have a conflict because technically LPT1: does not use
IRQ7!.
     The Parallel printer processor (the actual number escapes
me) contains a printer control register which enables the chip
to transmit an interrupt to the interrupt controller as IRQ7,
then onto the main processor as Int 0x0F. By default the parallel
printer processor does not enable it's interrupt line therefore
no Int 0x0F's will be sourced from the printer controller chip,
thus enabling other devices to use the actual IRQ7.

     Note, this applies to COM ports also which by default do not
route interrupts to the system bus, although COM's software
usually enable this feature as it make monitoring COM port
activity easier than polling the serial UART, thus probably
getting the sound card slighty confused!.