Hi,
Locate your spectrum.ini file within your mame installation folder and overwrite the scripting options part with this..
#
# SCRIPTING OPTIONS
#
autoboot_command j""\n
autoboot_delay 4
autoboot_script
console 0
plugins 1
plugin
noplugin
Then when mame has booted into the Spectrum and the sequence is complete press "F2" to simulate pressing play on the tape, I am pretty sure this can be automated too, but unsure how to make it happen, even though i have it auto playing tapes on other systems.