Lilongwe is unfotunately a bit of a shithole. For a capital city there is scarily little to do there, however: eating out - Mamma Mias, good Italian food, Don Brionis - excellent all round meals, Portugese Club - fine Chinese.
Avoid the Nature Sanctuary, nauseating and dangerous.
For weekends your best bet is the Northern Lakeshore. Ngala, Kande, Makuzi and Nkwazi are all stunning, stunning spots and only 4/5 hours drive. Salima/Senga Bay is closer but not so nice in my opinion although Cool Runnings is a great place to stay in Senga Bay.
If you get a chance see Mulanje/Zomba and Liwonde in the South although for wildlife you're best heading for South Luangwa, just over the border in Zambia. Kiboko Safaris put together some great packages out that way.
Anything else I can help with?, let me know.