For existing workbooks...........yes.
Create a style for each sheet by simply formatting or by Format>Style> and
create your own.
If you mean in any new workbook.
Open a new workbook and custimize/format each sheet as you wish.
File>Save As Type: scroll down to Excel Template(*.XLT) and select. Name
your workbook "BOOK"(no quotes). Excel will add the .XLT to save as
BOOK.XLT.
Store this workbook in the XLSTART folder usually located at........
C:\Documents and Settings\username\Application Data\Microsoft\Excel\XLSTART
This will be the default workbook for File>New or the Toolbar button
File>New or CTRL + n
WARNING................Do not use File>New...Blank Workbook or you will get
the Excel default workbook.
NOTE: Existing workbooks are not affected by these settings.
You can also open a new workbook and delete all but one sheet. Customize as
you wish then save this as SHEET.XLT in XLSTART folder also. It now becomes
the default Insert>Sheet.
More can be found on this in Help under "templates"(no quotes).
Instructions are for Excel 2003 and earlier.
2007 is similar except you would save as BOOK.xltx and SHEET.xltx
New File Icon or CTRL + n in 2007.