yeah,unaweza, no need of buying wireless router but your pc needs to have wireless network interface card
i hope unatumia windows 7.if it is
connect your modem kama kawaida.
create new network,yaani select Adhoc network, set up your security key if you want,if not go next,then wakati unaset chini utaona sehemu imeandikwa enable internet sharing,tick hapo and click ok,
ur done, enjoy your wireless interent