I have a Dell Vostro 420 dual core configuration system. I installed windows XP 32bit version with 3 partitions. Now I am planning to install Windows 7 64bit version on my current c:\ OS drive with out any effect to other 2 partitions. Can I do it like that. Can I get those 2 partitions without any conflicts.?
Are you saying you want to wipe out XP and install Windows 7? I'm assuming XP is on your C: drive/first partition. If so, just install it on your first partition if you don't want to keep XP. However, because you are going from XP to WIndows 7, you cannot do an inplace upgrade. You will have to do a fresh install of Windows 7 and then reinstall all your apps.
If you want to keep the XP partition, then you'll have to install Windows 7 on a different partition and then it will dual boot.
Also, be sure to backup your user profile using Easy Windows Transfer BEFORE you install Windows 7 so you can transfer your documents and files in your profile back to Windows 7.