nawk -F': *' '
$1=="Increment By"          { Inc = $2; next }
$1=="Max Value"             { Max = $2; next }
$1=="Related Table"         { Tbl = $2; next }
$1=="Related Table Column"  { Col = $2; next }
$1=="Sequence Name"         { Seq = $2; next }
$1=="Start With"            { Sta = $2; next }
END {
    fmt =     "<?xml version=\"1.0\"?>\n";
    fmt = fmt "\t<Sequence SeqName=\"%s\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\">\n";
    fmt = fmt "\t\t<SeqArea>appl/misc</SeqArea>\n";
    fmt = fmt "\t\t<SeqData>\n";
    fmt = fmt "\t\t\t<IncrementValue>%s</IncrementValue>\n";
    fmt = fmt "\t\t\t<MaximumValue>%s</MaximumValue>\n";
    fmt = fmt "\t\t\t<StartValue>%s</StartValue>\n";
    fmt = fmt "\t\t</SeqData>\n";
    fmt = fmt "\t\t<SeqDocs>\n";
    fmt = fmt "\t\t\t<SeqDesc>some description.</SeqDesc>\n"
    fmt = fmt "\t\t</SeqDocs>\n";
    fmt = fmt "\t\t<UseColumn TabName=\"%s\" ColName=\"%s\"/>\n";
    fmt = fmt "\t</Sequence>\n";
    printf fmt, Seq, Inc, Max, Sta, toupper(Tbl), toupper(Col);
}

' inputfile

#Begin
Increment By:1
Max Value:999999
Related Table: Dummy_table
Related Table Column: dummy_id
Sequence Name: dummy_table_1SQ
Start With:1
#End

<?xml version="1.0"?>
        <Sequence SeqName="dummy_table_1SQ" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
                <SeqArea>appl/misc</SeqArea>
                <SeqData>
                        <IncrementValue>1</IncrementValue>
                        <MaximumValue>999999</MaximumValue>
                        <StartValue>1</StartValue>
                </SeqData>
                <SeqDocs>
                        <SeqDesc>some description.</SeqDesc>
                </SeqDocs>
                <UseColumn TabName="DUMMY_TABLE" ColName="DUMMY_ID"/>
        </Sequence>