How can I resize hard drice "C" on lapto

Hello,
I had a problem I bought a laptop before couplw of months its dell inspiron 1525-122B
Its a nice pc but I really want to use windows XP not Vista. So in that case I had only one big hard drive its "c" and its large 225GB, and couple of other drives one is for recovery and others ar hidden so I may say that I use only "c"
I decide to resize that drive "C" and to make some other particion where Ill put windows XP but Ill keep my Vista in any case. After I try with Xp Ill erase Vista immediatly.
It was a good idea but I couldnt resize "C". I already try with disk managment it give me only 166mb to resize. I was disable paging file size and system restore because system told me that in taht case Ill have more space.
But it doesnt work, then I try with Particion expert 2003- it doesnt have acces to my hard drive,
then I try with Acronis Disk Director Suite 10.0.2117 which is better but the system doesnt let on the program to install it. I just enter the key its starts installing and just before the end it coing back and told me to try again.
After that I try with diskpart.exe on start menu, its was told me that I had one particion which is full and doesnt have free space.
I was so suprice actually I had 160gb free space but the system told me that my space is full ????
And last time I try with Paragon Partition Manger from Hirens boot cd, it was told me that I had 160gb free but when I try to resize it tell me "error no free space (cant create particion of request size)", I try event to make some little particion only 4gb which is enought for my XP but no it ws not acceptable.

I really hope to help, I try to as so many people in Bulgaria. Without result.