Actually, now that I think about it.. even if first and last name are in the same field or variable, as long as middle name/initial are not being used, you can still do it, simply.
fullname = "Reese Witherspoon";
concat = left(ListGetAt(fullname,1," ",true),1) & left(ListGetAt(fullname,2," ",true),5);
^_^
UPDATE: Minor modification. This works as long as the last name isn't something like "Van ****" or "Van Zandt". SOOOOOOOO, check the list length (with " " as delimiter) and if it's greater than two, join positions 2 through x together, removing all spaces.
fullname = "Dick Van George Jettson"; // It didn't like D y k e.. sigh..
thisLen = listLen(fullname," "); // 4 if (thisLen eq 2){ concat = left(ListGetAt(fullname,1," ",true),1) & left(ListGetAt(fullname,2," ",true),5);}else{ concat = left(ListGetAt(fullname,1," ",true),1); lastname = ""; for(i = 2; i lte thisLen; i=(i+1)){ lastname &= ListGetAt(fullname,i," ",true); } concat &= left(lastname,5);}