James Preston: Private, Co. E, 36th Alabama Infantry. Only one muster roll card with any information. He resided in Washington County, Alabama. The muster roll card is part of a record of prisoners of war parolled in May, 1865. The record states that he is part of the regiment that was surrended at Citronelle, AL by Lt. Gen. R Taylor, CSA to Maj. Gen. E.R.S. Canby on May 4, 1865. He was parolled on May 20, 1865. That is all there is to this record.
James A Preston: Private, Co. I, 4th Alabama Infantry. He was listed as a student and was killed at Manasses on July 21, 1861. I believe there are about 5 muster roll cards for this individual.
J.A.L. Preston: There are 23 muster roll cards for this individual who is listed variously as James A. Preston, J. A. Preston, J. S. Preston, J.A.L. Preston and J.A.S. Preston. He was from Decatur, Morgan County, AL and served in Co. E, 9th Alabama Infantry. He was wounded and spent some time in the hospital in Richmond, Virginia. He rose to the rank of Sgt.
Those are the only James Preston's from Alabama I found in the Confederacy. I did not check the Union records as you indicated he served the Confederacy. If you are not certain about that, I will gladly check the Union records. The only James Preston I found for the Confederacy in Tennessee was a James C. Preston.
As for Lt. Thomas Pleasant Preston, I found one man named Thomas P. Preston who served the Confederacy in Co. C, 42 Alabama Infantry as a 2nd Lt., promoted to 1st Lt. He was captured at Corinth, MS on Oct. 4, 1862 and was exchanged on Nov. 8, 1862. He was wounded slightly and captured at Vicksburg, MS when that city was surrendered to U.S. Grant on July 4, 1863. He was killed in action on May 15, 1865.
If you provide your e-mail address, I will gladly forward any of these muster roll cards you desire.
Regarding learning to do the research, I would suggest a couple of resources: first is the Civil War Soldiers and Sailors System managed by the National Park System. The link follows: http://www.nps.gov/civilwar/soldiers-and-sailors-database.htm. This is a free database and is a good place to start, but would only provide a list of names and units. I also recommend Fold3.com as you can search by Union or Confederacy, by state for any name and will come up with all the results that have been entered. Fold3.com is connected with the National Archives. This service requires a fee, but that is not too steep. If you are a member of the Sons of Confederate Veterans you can get a discount, I believe. On a side note, if you are NOT a member of the SCV, I would encourage you to join as this is a great way to honor your ancestors and to help preserve Civil War history. I personally belong to both the Sons of Confederate Veterans and the Sons of Union Veterans of the Civil War.
As for further information of your ancestors prior to and following the war, I would suggest a membership to ancestry.com.
Again, if I can be of any further assistance to you, please let me know. I am happy to copy and send the muster roll cards.
Allen Davis