The only way I've been able to do that is like this:
rem Setup display
set display mode 640,480,32
set window off
rem Make floor
make object plain 1,500,500
xrotate object 1,90
position object 1,0,0,0
color object 1,rgb(0,200,0)
rem Make player
make object cube 2,50
color object 2,rgb(200,0,0)
rem Make mouse
make object cube 3,50
hide object 3
rem Initialise variables
x#=0
y#=25
z#=0
mx#=0
my#=25
mz#=0
targetx#=0
targety#=25
targetz#=0
rem Setup manual synchronisation
sync on
sync rate 0
rem Start main loop
do
rem Control mouse
if object screen x(3)<mousex() then mx#=mx#+1
if object screen x(3)>mousex() then mx#=mx#-1
if object screen y(3)<mousey() then mz#=mz#-1
if object screen y(3)>mousey() then mz#=mz#+1
position object 3,mx#,my#,mz#
rem Control movement
if mouseclick()=1 and click=0
targetx#=mx#
targetz#=mz#
oldang#=object angle y(2)
point object 2,targetx#,y#,targetz#
targetang#=object angle y(2)
yrotate object 2,oldang#
click=1
endif
if mouseclick()=0 then click=0
if x#<targetx# then x#=x#+1
if x#>targetx# then x#=x#-1
if z#<targetz# then z#=z#+1
if z#>targetz# then z#=z#-1
position object 2,x#,y#,z#
yrotate object 2,curvevalue(targetang#,object angle y(2),30)
rem Control camera
set camera to follow x#,y#,z#,0,200,200,3.5,0
point camera x#,y#,z#
rem Setup manual synchronisation
sync
rem End main loop
loop
It needs perfecting but it should help. Better still; buy pro.