I have a 80GB hard disk with WinXP already installed.I had tried installing Fedora 10 earlier without creating new partitions(real foolish and ignorant of me 
o ) and tried creating partitions using Fedora10 bootable.It didnt work.Then I created a free partition and again tried installing Fedora10 using same procedure of creating 'Custom layout'.This time it again didnt work and in addition also corrupted Windows.I reinstalled Windows XP and used Partition magic to create a free partition of 20 GB in ext3 format.Now when i try to boot Fedora 10 the screen says 'Loading initrd.img and the PC restarts.This keeps on going. I tried with Fedora 12 bootable but now my PC says "LOADING initrd.img' and then says 'not enough memory' and nothing goes forward.
My windows working fine.My hard disk (80GB,two 20 GB parttions in NTFS,one 20GB partition in FAT32 and one 20GB partition in EXT3 format).RAM 512MB
Help 
as i want dual boot in my system ...
Does the fedora CD/DVD have memtest86 or memtest86+? If so, run that.
Have you checked the CD/DVD for integrity (Md5sum?)
Thanks Mark!!
But I have used the same DVD to boot on another machine..
Yes,as u said Fedora 10 had Mem86 test......and i used it....
I am not sure how to interpret the results and it shows some errors..
Does it mean the RAM is faulty?
The Windows is working fine.
If it shows some errors, i.e. outputting lines in red, you have some errors. Windows may not immediately use the bad sections when it boots the way Linux seems to.
Windows seems more forgiving about bad RAM. It will use the memory and that can cause flaky behavior that people attribute as "Oh, that's just Windows." I have seen that Linux does not tolerate bad RAM in the same way. If you had red lines on memtest86 or memtest86+ then, depending on the address of the bad area of RAM, you can usually isolate that to a particular stick of RAM.
For example, if it says that the bad area is at 1201MB and you have 2GB of RAM, in 1GB sticks, it is probably the 2nd stick starting from slot 0.