Your system has a hidden partition with Vista and all your drivers on it, you need to decide wether to keep this partition in tact (incase you want to install Vista again) or to delete it and use the whole drives available space making it one partition instead of two.
ONLY delete the recovery partition if you have a copy of windows XP that you OWN. otherwise if you have problems again, you will have to find a disk again.
You will need a copy of windows xp, set the bios to boot to the cd/dvd rom in the BIOS and boot the system with the xp disk, do a full install first delete any partitions (unless you save the hidden partition, then just delete the large partion)
Repartition the empty space , then format the drive, which you will be prompted to do after partitioning, then the cd will install windows. follow the prompts.
Once finished , go here http://www.acerpanam.com/synapse/forms/portal20.cfm?website=AcerPanAm.com&siteid=7117&areaid=2&formid=3394#results
and download the 5 XP drivers for your system, install the chipset andcpu driver , then proceed to the NIC, audio and video.
You will then need to install any programs you had installed before. keep in mind a vista version of software may not operate correctly on XP. windows xp is about 130 dollars for the disk , but you can find copys on ebay for around 90.
poast again if you need more help