Samsung Magician 4.9.7 I think is the last version that works on Windows XP and can do TRIM on demand. It supports very old SSDs only like 850 EVO. You also need AHCI driver, not SCSI driver in Windows XP. I was able to run it successfully in Windows 7 only with AMD SATA controller and EVO 850.
2nd option is to use Acronis True Image 2014. In menu Tools and Utilities -> Trim SSD. It seems to do it properly by rebooting and trimming on restricted boot. This works with old chipsets like nForce 4 which do not support AHCI. I use it with 860 EVO.
3rd option is to use USB key with Linux.
Pentium III 900E,ECS P6BXT-A+,384MB,GeForce FX 5600, Voodoo 2,Yamaha SM718
Athlon 64 3400+,Gigabyte GA-K8NE,2GB,GeForce GTX 275,Audigy 2 ZS
Phenom II X4 955,Gigabyte GA-MA770-UD3,8GB,GeForce GTX 780
Vishera FX-8370,Asus 990FX,32GB,GeForce GTX 980 Ti