I have tried that on more than one occasion. If you have the windows
disk the below directions work after you insert the windows disk and
select repair installation. The problem is the MBR (master boot record)
that was altered when lubuntu was installed.

It all depends on if grub (the boot loader) was installed by the lubuntu
disk/flashdrive.

I would just change the size on the Lubuntu install to a absolute
minimum and loose the 4gig to Linux unless I had an XP disk.