Well, Sniper, I believe you could install XP as far as the machine is concerned but there is a very limited number of drivers and utilities available from Toshiba for XP on this machine. You can see them--12--at THIS SITE for your machine.
If you have a big enough HDD and insist on proceeding, why don't you partition your HDD and install the XP in the new partition and if you have any problems, your original Windows 7 will still be available. Type Disk Manage in the Start/Search box and click on Create and Format Hard Disk Partitions.
P.S. Jerry Lippey, please step in here if I am the least bit misleading since you are the real expert on these matters.
C.B. Toshiba Sat. L675D-S7016 Win 8 PRO 64 Bit---Toshiba Sat. L775D-S7132 Win 7 PRO SP3 64 Bit which also has Virtual Machine with Win XP SP3---Toshiba Sat. L305-S5921 Win Vista SP2 32 Bit