Your first error deals with the fact that from your dll, the handle to your form is undefined. The dll and your application are not in the same address space, so using handle is undefined from your dll. The handle can be null, so it may be ok to just put zero (0) rather than a Handle.
Your second error is due to the fact that you do not include the unit where SW_SHOWNORMAL is declared. Include 'Windows' in the uses clause or you can put in the value that SW_SHOWNORMAL is defined to be: 1
Here is a list of the values defined:
{$EXTERNALSYM SW_HIDE}
SW_HIDE = 0;
{$EXTERNALSYM SW_SHOWNORMAL}
SW_SHOWNORMAL = 1;
{$EXTERNALSYM SW_NORMAL}
SW_NORMAL = 1;
{$EXTERNALSYM SW_SHOWMINIMIZED}
SW_SHOWMINIMIZED = 2;
{$EXTERNALSYM SW_SHOWMAXIMIZED}
SW_SHOWMAXIMIZED = 3;
{$EXTERNALSYM SW_MAXIMIZE}
SW_MAXIMIZE = 3;
{$EXTERNALSYM SW_SHOWNOACTIVATE}
SW_SHOWNOACTIVATE = 4;
{$EXTERNALSYM SW_SHOW}
SW_SHOW = 5;
{$EXTERNALSYM SW_MINIMIZE}
SW_MINIMIZE = 6;
{$EXTERNALSYM SW_SHOWMINNOACTIVE}
SW_SHOWMINNOACTIVE = 7;
{$EXTERNALSYM SW_SHOWNA}
SW_SHOWNA = 8;
{$EXTERNALSYM SW_RESTORE}
SW_RESTORE = 9;
{$EXTERNALSYM SW_SHOWDEFAULT}
SW_SHOWDEFAULT = 10;
{$EXTERNALSYM SW_MAX}
SW_MAX = 10;