If the big problem is knitting in the round, it's fairly easy to change to flat knitting with a seam. The main thing to remember is that you want your seam to be in the back, where it will be the least visible.
Just cast on the number of stitches called for on one regular straight needle. Then, instead of joining to knit in the round, just knit across and purl back.
In circular knitting, every row is knit in stockinette stitch. This is one of the reasons a lot of people prefer it. Knitting flat requires that you purl every other row.
If any shaping is required, count from the first stitch of the row to get the correct placement. (If you were knitting in the round, you would have placed a marker to show the beginning. The first stitch of the row is the same as the first stitch after the marker.)
You may want to add one stitch to the end to allow for seaming, but it probably isn't all that necessary. If it's one stitch smaller than the finished size called for in the pattern, it's not all that big a deal. It's your call as to whether you decide to add it or not.
Hope my answer isn't too simplistic. If you have any other questions, please ask--I'm always happy to help.