Or you can simply delete the existing partition and re-create it... if you have nothing you need to keep. If you have data on the drive that you'd like to hang on to, then ed's suggestion is the way to go.
Edit: Forgot to ask... what version of XP Pro? Original? SP1? SP2? I believe your XP install CD must have at least Service Pack 1 to be able to create partitions larger than 137GB. If you can see 137GB, then LBA is already enabled (as it is by default on newer Dells). You can use Acronis to "grow" the partition, but unless you have at least SP1 installed on your XP, it probably still won't recognize anything more than 137GB.