Problem with Excel Download

Hi everyone, i call the function GUI_DOWNLOAD to download an intern table into Excel format.

the problem is

a field for exemple tab1-f1 = '4.5', but after downloaded into excel, it turns out automatically into Date format. which shows. 04.May.(i used German office version).

by the way i define the intern table like

types: begin of ts_tval,

aubel(20),

posnr(20) ,

matnr(20) ,

vbeln(20) ,

posnr_re(20) ,

atinn(20) ,

atnam(20) ,

atkla(20) ,

atwrt(20) ,

atflv(20) ,

end of ts_tval,

data lt_tval type table of ts_tval.

then the field will be valued as:

lt_tval-atwrt = cawn-atwrt.

anyone can tell how to set the format of excel cells???

thanx a loooot!!!!!!